Messi has fallen short of expectations in Ligue 1, having scored only twice in 15 league outings so far.
As a result, the Argentine has faced significant criticism from the press, with some even suggesting he may never replicate the stunning form he exhibited at FC Barcelona.
Former France star Emmanuel Petit, himself a former Blaugrana player, is one of the seven-time Ballon d'Or winner's latest critics, having claimed that the 34-year-old's performances are on a decline.
"I feel genuine pain when I watch Messi on the pitch. We all want him to succeed, to take our hand and tell us a story like he told thousands in Barcelona," Petit said on an RMC Sport broadcast.
"I don't want to pit Messi against [Kylian] Mbappe. But for several months, we have been witnessing the death of one king and the rise of another.
"I know that this guy has an oversized ego, but at some point, he will have to understand that as long as he is not well, especially mentally, he will not be able to become the Messi of Barça again.
"I hope that by the end of the season, we will be able to see the great Messi intermittently, but over time it is no longer possible."
Messi has, however, been more prolific in the UEFA Champions League, in which he has scored five goals in six appearances so far this season.