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This year as maybe not a good year for Messi because they didn't respect him as they should respect him, in fact, he didn't get what he had to get from the fans and that's why the performance of this player was not well enough. I think Messi is still a good player and he could help PSG much better than this if they helped this player and gave him a good atmosphere.
Of a truth it wasn't a great year for Lionel Messi at PSG but I think it's high time we start to accept the fact that Messi is aging and wouldn't still be performing like the Lionel Messi of 6 to 10 years ago.
He exhausted much energy in the world cup Last year and after the World Cup tournament, he also can back to Paris and still did quite well. PSG fans didn't respect him in his last days at the club which is very poor from them
This season for Messi is like a fighting machine that has lost ammunition where he cannot do anything to attack considering his old age and declining game performance.
As you said he spent all his energy in the last World Cup so when he came back to PSG he lost some playing power.
But he didn't notice his declining form and instead wanted to play for a higher fee so some people couldn't respect him.
If observed closely, it is indeed Messi's time to retire and hope that he can see Messi play even better will never be achieved.