It is "by no means certain" that Moeen Ali will be available for England's tour of Sri Lanka, according to Ed Smith.

Smith, the national selector, admitted there was "no time frame" for Moeen's return to Test cricket after he was, once again, absent from England's squad for the tour of South Africa.

Moeen asked for a break from Test cricket at the end of the 2019 English summer and, despite conversations with Smith, fellow selector James Taylor and England captain Joe Root in recent days, remains unavailable by his own choice. His absence does not extend to white ball cricket and it would be a surprise if he did not return to the England party for the limited-overs part of the South Africa tour.

Also read: Bairstow, Anderson, Wood return to England Test squad

"He asked to take a break from Test cricket at the back end of last summer and that is what has happened," Smith said. "At this stage we don't know when he will return to being available for Test cricket but it's our hope that he does. We all know that Moeen is a talented and valued cricketer for England. But we don't know if and when that might happen."

Hopes that Moeen could return for the Sri Lanka tour, where he played a key role in England's 3-0 victory a year ago, in March were not boosted by his inclusion in the PSL draft. The competition takes place at the same time as the tour. But while Smith admitted there were no guarantees Moeen would return for that tour, he felt it was possible.

"I don't think it's ruled out and it's also by no means certain he will be available," Smith said. "At the moment there's no time frame. But what I did discuss with Moeen - what we all discussed with him - was our aspiration that he's available to play Test cricket for England. He's a valued England cricketer. From my point of view and a selection view, the sooner he was available the better and that would include Sri Lanka.

"He did say that there are more Test runs and more Test wickets in him and that was very encouraging. It's disappointing when a player of Moeen's ability and track record is unavailable for selection. In an ideal world, we'd like Moeen to be available."

While Moeen lost his place in the England side during the Ashes - and the Test part of his central contract at the end of the season - his potential value as a Test cricketer may have been reappraised a little in his absence. Not only does his non-availability leave England with the prospect of a diplodocus-length tail - Jack Leach, James Anderson, Stuart Broad and Jofra Archer seem most likely to feature from No. 8 to No. 11 in South Africa - but his relative potency with the ball has been missed. After 60 Tests (and 181 wickets), he has a better strike-rate (60.6) than hugely respected spinners of the past such as Jim Laker (62.3), Derek Underwood (73.6) and Hedley Verity (77.5). Leach, after 10 Tests, has a strike-rate of 60.9.

Although Moeen was nowhere near his best with the bat - he averaged 10 in five Tests in 2019 - in his most recent Tests, England remain hopeful that a return to his best will give them greater penetration with the ball and an easier balance in the team. England claimed only 21 wickets in the two Tests in New Zealand and went into the second Test without a front-line spinner for the first time since 2013.

Smith also defended the selection of Ollie Pope as England reserve keeper for the New Zealand tour, but declined to clarify who had been selected as reserve keeper in South Africa with Jonny Bairstow recalled to the squad.

"That would be a question for the captain and coach to answer," Smith replied when asked who would keep should Jos Buttler suffer another back spasm on the morning of a Test in South Africa. "They've got pretty good options.

"We were very clear when we discussed the tour party to New Zealand that we were going to take a 15-man party for a very short time. We had discussed the possibility of a last minute injury to Jos and we were comfortable with Pope keeping wicket. He has kept a great deal in his life. I've seen him keep a lot, James Taylor has seen him keep a lot and not only for the Lions but for Surrey.

"In the last 10 years that's the only last minute injury to a keeper. Jonny got injured in a different format in Sri Lanka, which brought about a change when Ben Foakes came in. But for it to happen at the 11th hour is very unlikely. But it was discussed and we were comfortable with Pope coming into the side if a last minute injury happened to Jos. We knew he was a very capable keeper."

"Bairstow has been picked as someone who could add value to an England Test team. He's a talented batsman who has scored a hundred at No. 3 as well as hundreds lower down the order. And he's kept wicket in many games for England so he covers both of those possibilities.

"Since the moment he was selected as a batsman for England - he was the first of his generation to be selected, in 2012 - he has a non-Test first-class average of 57. He wants to get back into the team and he knows when he's playing well he has a number of routes."