He missed Barcelona's 5-1 league rout of Madrid in October because of a broken right arm.
"I have not seen Leo Messi, we will see how it is, if it can be done, if it can be completed and if he is fit".
"They were in a completely different place then, which needs to be taken into consideration", he said of Madrid, who have won seven of their last eight matches in all competitions.
"The most important thing is for the player to tell you that he is ready", coach Ernesto Valverde said.
Asked later whether doubt over Messi's participation would affect his side's preparation for the game, Solari smiled and added: "Not at all". The tie is wide open, we have really good players.
But Barcelona remain stronger now and I expect them to win and take a good lead into the second leg, on their way to the Copa del Rey Final.
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That said, the players were visibly exhausted after the match but have had one extra day's rest to prepare well for the first leg. Barcelona's fixtures were certainly a lot more demanding that Real Madrid's, but the Whites did not have an easy run either and hence, a day extra will make a huge difference especially for a match as massive as this one.
"They are usually strong at Camp Nou, they play well here".
If Messi manages to recover even partially, I think the decision will be up to him more than the manager, given his status at the club.
Barcelona are aiming to win a fifth-straight Copa del Rey with Valencia or Real Betis awaiting them in the final should they beat Real Madrid.
Ousmane Dembele, who had trained separately on Monday, also re-joined his teammates in Tuesday's practice, but he was not included in the squad list for Wednesday's game. We have the player we believe is the best in world but they also have great players.
Click through the gallery above to see the 10 most clinical goalscorers in El Clasico history, according to Transfermarkt.
"In a semifinal between Barca and Madrid there's no favourite".