Ole Gunnar Solskjaer has been involved in top-level football long enough to identify a pivotal moment when one arrives, so the Manchester United manager should not be in any doubt as to the challenge he faces over the coming days. The Norwegian is fighting for credibility, both within the dressing room and among the supporters, and it is not simply about what happens with Paul Pogba.

It has now become the norm for United that their preseason preparations are played out to the backdrop of a seemingly endless saga and, as Solskjaer's squad landed in Perth on Monday for the first leg of their summer tour of Australia, Singapore and China, Pogba had already ensured that he would be the central figure in this year's Old Trafford soap opera. The France midfielder, who posted video on social media over the weekend of his personal running sessions in New York's Central Park, has already spoken of his desire for a "new challenge" this summer, while his agent, Mino Raiola, confirmed last week that his client was seeking to leave United before the start of the 2019-20 season.

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United have insisted that Pogba is not for sale, but sources have told ESPN FC that Solskjaer and his coaching staff were prepared for a public war of wills involving the club and the player, knowing that every decision and every comment in the media would have to be carefully considered and delivered in order to maintain some element of control over the situation. But the Pogba saga is likely to be the easy part of the summer for Solskjaer. If he persuades him to stay, Solskjaer will have kept his best player, yet if he sanctions his departure, the United manager will instantly receive the backing of a fan base that has grown tired of the 26-year-old and his unconvincing performances on the pitch and, at times, infuriating behaviour off it.

Sources have told ESPN FC that Pogba is also not universally popular among the playing squad, with some teammates exasperated by the £89 million signing from Juventus and his failure to live up to his reputation as one of the world's best midfielders. But while there is scepticism over Pogba's ability, or desire, to make a difference, there is also a group of players at United who want to see more from Solskjaer and his coaches in order to be convinced that the team is heading in the right direction.

One source has told ESPN FC that there were concerns within the squad's foreign contingent as early as February -- when Solskjaer was still unbeaten in his role as caretaker-manager -- that the approach under the former Cardiff City manager was "too British" and lacking in continental expertise. The same source has claimed that last week's training regime was "just running, running, running," with players forced to do double sessions on their first week back in preseason following Solskjaer's decision to bring the squad back as early as July 1 to start preparations for the new campaign.

Complaints about a heavy training workload are likely to receive short shrift from Solskjaer and his coaches, with ESPN FC reporting in May that Solskjaer and his assistant, Mike Phelan, had been dismayed by the poor fitness levels of the squad following their arrival in place of the sacked Jose Mourinho last December. Solskjaer and Phelan are determined to ensure that a vast improvement on basic fitness levels are dealt with as a priority, so there are likely to be more demands placed on the players during their first week on tour in Australia.

However, one of the first mistakes made by David Moyes during his ill-fated 10-month reign as manager in 2013-14 was to focus too heavily on fitness rather than technique and the Scot struggled, and ultimately failed, to convince the players of his fitness-first approach.

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Solskjaer has also travelled to Australia knowing that Pogba is not the only member of his squad who wants to leave. Romelu Lukaku is keen to secure a move to Italy with Inter Milan, David De Gea continues to resist United's attempts to tie him to a new contract, while Nemanja Matic is aware of interest from Inter and AC Milan and prepared to leave Old Trafford for the right offer.

Having allowed Marouane Fellaini to leave for China in January before seeing Antonio Valencia and Ander Herrera leave as free agents this summer, Solskjaer's squad is now arguably weaker than when he arrived, with only Swansea youngster Daniel James and Crystal Palace right-back Aaron Wan-Bissaka being added since the end of last season.

Attempts to sign a new centre-half after seeing the team post United's worst defensive record in Premier League history last season have so far failed to come to fruition, while interest in Newcastle youngster Sean Longstaff has yet to result in a bid, despite the St James' Park outfit being in a state of flux following the exit of manager Rafa Benitez.

After a dismal end to the 2018-19 season, which saw United win just two of their last 12 games in all competitions, Solskjaer was always going to be under pressure to turn the tide this summer. But before a ball has even been kicked in preseason, he is already on the back foot thanks to Pogba, the doubts of some of his players and the failure to make more substantial changes to his squad. So what happens in Australia, Singapore and China over the next two-and-a-half weeks will be crucial for Solskjaer and his hopes of enjoying any kind of success at Old Trafford.