Messi has recovered from a knee injury and is expected to return for Paris St Germain against Manchester City in a rematch of last season's Champions League semifinal.

Speaking at a press conference on Monday, PSG coach Mauricio Pochettino did not reveal his line-up but said the Argentina star was fit to play.

Messi had previously been ruled out of two consecutive league games following a knock to his left knee on his home debut earlier this month.

Against City, he will be up against Guardiola, who was Messi's coach at Barcelona between 2008 and 2012 during an exceptionally fruitful spell.

Among their many titles, the pair won the Champions League in 2009 and 2011, with the six-time Ballon d'Or winner scoring in both finals.

In total, Messi scored 211 goals in 219 games in all competitions under Guardiola, who reportedly failed to secure his transfer to City during the summer.

"That was a little bit of a surprise for everyone, but what happened has happened," Guardiola said when asked about Messi playing for another club than Barcelona.

"A few years ago, you could not imagine. But football, you never know. Life, you never know what is going to happen in a short time."

Messi, 34, has featured in only three matches for PSG and is still chasing his first goal following his shock move.

In addition to the Lyon game where he got injured, Messi also made a substitute appearance on his debut against Reims and started in attack alongside Kylian Mbappe and Neymar in the 1-1 draw at Club Brugge in their opening Champions League group game.

"Let the player work, let the player adapt and start to feel at home," Pochettino said.

"He was at Barcelona for 20 years. It is normal that he feels at home in Barcelona. Now everything is new. For sure, he is going to succeed."

With Messi fit, Pochettino could field his formidable attacking trident. Although the trio did not impress against Brugge, Guardiola said he does not have a recipe to stop them.

"They are so good! This amount of talent, together, it's so difficult," he said.

"We are going to try to defend well when we don't have the ball, and make them run when we have the ball."

City, who won 2-1 in Paris and 2-0 at home in last season's semi-final, are unbeaten in their five matches with PSG, but Guardiola brushed off any notion his players will start with a psychological edge.

"This is a new season, a new challenge. I don't care if you win three games in a row, or lose three games in a row, this is a new one," he said.

Australian Associated Press