Lionel Messi has been impressed by Cristiano Ronaldo's start to life back at Manchester United and retains fond memories of their "beautiful" rivalry in LaLiga.

Portugal international Ronaldo has scored nine times in 13 appearances for United since making a sensational return to the club at the end of August.

That is a goal tally bettered by only six other players from clubs in Europe's top five leagues over the same period, with Bayern Munich's Robert Lewandowski (17) leading the way.

Despite Ronaldo's form and ability to bail out his side with late goals, United have endured a poor campaign and sacked manager Ole Gunnar Solskjaer on Sunday.

But with less than half of the campaign played, Messi does not believe a Ronaldo-inspired United can be entirely ruled out of the Premier League title race.

"They're a very strong team with great players," he told Marca. "Cristiano already knew the club, but that was in another stage and now he has adapted in an impressive way.

"From the beginning he has scored goals as always and had no problems adapting. In the Premier League, United have not been as good as we all thought.

"But it is a very difficult and even competition in which things take a lot of turns. After December it changes a lot and anything can happen."

Cristiano Ronaldo has scored nine times since returning to Manchester United

Messi and Ronaldo have won 11 of the last 12 Ballons d'Or between them – the exception being Luka Modric's triumph in 2018 – in a period that has been dominated by the pair.

Not only have the superstar forwards fought for individual honours, they also battled it out for domestic and European team honours during nine years together in LaLiga.

While Ronaldo has long since departed Real Madrid and Messi is no longer at Barcelona, the latter believes their rivalry will live long in football folklore.

"It's been a long time since we stopped competing in the same league," Messi said. "We competed individually and as a team for the same goals.

"It was a very beautiful period for us and also for the fans because they enjoyed it very much. It is a beautiful memory that will remain in the history of football."

With Messi aged 34 and Ronaldo approaching his 37th birthday, the likes of Kylian Mbappe and Erling Haaland are now considered the next big talents in world football.

Mbappe is a contender for this year's Ballon d'Or after scoring and assisting a combined 50 goals in 46 appearances for Paris Saint-Germain in all competitions in 2021.

Only Lewandowski (58) has been directly involved in more goals this year, but PSG risk losing Mbappe to Madrid next year when his contract expires.

Messi, now a team-mate of Mbappe's following his shock free transfer from Barca in August, is unsure whether the France forward will still a PSG player next season.

"The truth is I do not know," he said. "Only he knows what he has in his head and what he is going to do. I can only say that I am happy that he has stayed here this year.

"He is a very important player for us and to fight for the objectives we have. He is fully focused on our goals. And then he will decide what he will do when the season is over."