Jos Buttler admits that he cannot continue to be picked on "potential" alone at Test level, after being retained in England's squad for next month's tour of Sri Lanka despite an off-colour showing during the recent Test series in South Africa.

In the midst of an otherwise upbeat run of performances from England's new-look Test team, Buttler's form was a notable exception. He mustered 115 runs in seven innings, with a highest score of 29 - a run that evoked a similar collapse in red-ball confidence on the tour of UAE in 2015-16, after which he played just three more Tests in the next three years.

And in the wake of England's 3-1 series win, there was inevitable speculation about Buttler's future as a Test cricketer - especially given his integral importance to England's white-ball fortunes, both in winning last year's World Cup on home soil and in challenging for three more titles in the next three years: back-to-back 20-over World Cups in Australia and India this winter and next, before the defence of England's 50-over title in 2023, by which stage he may well be the white-ball captain.

Buttler himself, however, insists he still has the drive to succeed in Test cricket, which he describes as "the best form of the game", and says that, despite a Test record that now comprises a solitary century in 73 innings, at an average of 31.74, he retains the "massive self-belief" required to become a world-class player across all three formats.

"I'm very committed to Test cricket," Buttler said. "It's the best form of the game, it's the hardest form of the game. That's what makes it - when you have good moments - the most rewarding. You want to be a part of that.

"My performances may have meant that decision would be taken out of my hands. But fortunately for me I'm on the tour [to Sri Lanka] and really excited about it. I enjoyed the last tour there that we won back in November 2018. I've got good memories from that tour and looking forward to going back."

Though he finished the South Africa tour on a relative high, with a 23-ball fifty in England's series-clinching victory in the third T20I, Buttler acknowledged that his form throughout the tour had not been where he wanted it to be. However, he insisted it was an "easy assumption" to put that down to any sense of a post-World Cup hangover.

"I've got massive self-belief in myself. I'm too old now to get picked on potential but I feel that I haven't got to the level I know I can get to, and that's a big driver for me"

Instead, he insisted that the challenge of "managing your energy" was something that all the world's top players had to get their heads around as they seek to make the most of their finite years at the top level of the sport.

"Definitely a lot went into the World Cup, not just that summer but for four years," Buttler said. "Probably the realisation of it coming together and achieving that, it confuses you a little bit - that's been your clear cut-off for a long time, then that's done. So you've got to quickly reassess.

"But at the same time, I maintain I just haven't played as well as I'd like and that's through decision-making, probably."

There's no let-up in Buttler's 2020 schedule. He sets off for Sri Lanka with the Test squad in early March before linking up with Rajasthan Royals in the IPL immediately after the conclusion of the second Test in the first week of April. Then he returns to England for three Tests against West Indies in June, by which stage the inaugural season of the Hundred will be coming into view. Further international engagements against Australia and Pakistan will complete the English summer, by which stage the T20 World Cup will be looming large. It promises to be a lot of chopping and changing if Buttler truly believes he can compete on all fronts.

"I think trying to manage your energy, it's actually a real skill of the best players around the world," he said. "Learning how to peak at the time you walk to the middle is a massive skill that comes with experience, but you can learn that from watching guys go about it and trying to work out how you do that authentically for yourself.

"Of course you need to find breaks in your schedule, because your mind is your biggest asset, and you need to make sure you can bring that to the best place when you turn up to games of cricket. But there's a crop of guys who are the best players in the world and they're the best players across all the formats.

"I've got massive self-belief in myself, and a lot of it is about fulfilling potential," he added. "I'm too old now to get picked on potential but I feel that I haven't got to the level I know I can get to, and that's a big driver for me. That's my aim every time I turn up to practice, to try and get better and try and reach that level I am capable of. I've always maintained that belief."

Instead of the prospect of any outright rest, Buttler believes that a change will do him just as much good, and said that the chance to cut loose in the recent T20I series came as a "big relief" after a run of ten Tests in a row against Australia, New Zealand and South Africa.

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"I love T20 cricket and it allows you to go out without as many consequences and you can take more risks and move the game on," he said. "To play in that white-ball team again was great because that is the most fun team I have played in for a long time, so that was a great change up.

"I can't think of any times I've played well in Test cricket and gone out and been really aggressive in the way I do in the white-ball game," he added. "In white-ball cricket it might look like risky shots but it doesn't feel like a risk because of the way you break down the probabilities of the game.

"The same is the case in Test cricket, it is about risk management I think. And it is about managing your time when you are waiting to bat. You've got to be aware of what is going on in the game but it is about saving energy as well.

"Maybe if I look back to when I first lost my place in the Test team, I probably listened to too many people," he added. "Everyone's got an opinion on how you should play, and if you're not good with how you manage that, you can confuse yourself, which I certainly did four or five years ago.

"Maybe in South Africa I did that a little bit in terms of, after the first game, thinking I'm going to come out and counter-attack. When actually, you've just got to play the situation in front of you and react best and, as an individual, play how you see best according to that. I maybe didn't do that as well as I would have liked.

"The main skill, and the biggest one that I do well when I'm at my best, is making sure that when I walk out to bat I access being in my zone, whether I've been waiting for six hours or just have a 10-minute turnaround in a T20.

"When I walk out to bat, if I'm in the best frame of mind, that allows me to perform. And looking forward to Sri Lanka. I will try and do more of committing to my way, whether it's trying to block 1000 balls or slog 1000 balls. If that's what I want to try and do, I'll do it."