The Barcelona legend and all-time top goalscorer, currently at Paris Saint-Germain, is likely to leave the French side at the end of his contract in June, a club source told AFP on Tuesday.
Some fans sung Messi's name outside the stadium before the clash with Real Madrid and many joined in after 10 minutes of the match, representing the Argentine's shirt number at Barca.
"Messi is living history at Barcelona, he's the best player in the history of football," said sporting director Mateu Alemany before the Clasico on Wednesday.
"He's at PSG fighting for titles and we are fighting for ours. In the future, we'll see what happens."
World Cup winner Messi, who will turn 36 in June, joined PSG in 2021 on a two-year deal which expires at the end of this campaign.
The forward has been whistled in recent weeks by some of PSG's own fans in Paris, frustrated at the club's Champions League elimination by Bayern Munich.
His form has dipped since he led Argentina to glory at the World Cup in Qatar at the end of last year, with some seeing him as a symbol of PSG's mistakes in signing star names at the expense of building a competitive team.
Barcelona have been openly courting Messi, hoping to persuade the forward to return to Camp Nou two years after he left the club where he won four Champions League titles.
Messi left Barcelona when the club could not afford to renew his contract.
"I would love it if he returned," Barca vice-president Rafael Yuste said last week as he admitted there had been "contact" with Messi.
