Barcelona to make late call on Messi for Copa Clasico
Messi was hurt in the second half of Barca's 2-2 draw against Valencia at the weekend, after he had scored twice to draw the LaLiga leaders level from two goals down.
Valverde described the injury, which appeared to concern Messi's thigh, as a "small problem" when he spoke to the media after the game, and the forward reportedly missed training on Monday.
Messi was absent when Barca demolished Madrid 5-1 at Camp Nou in LaLiga at the end of October, but Valverde will give his captain every chance to be available for Wednesday's game.
"I haven't had today's training session so I can't answer," Valverde said when asked if Messi would be fit.
"There's still a training session to go, we'll see how he has and if he can complete the session. Then we'll make a decision.
"I don't think it changes everything, there's never a favourite in a semi-final between us and them, it'll be an open game, we've got very good players and a player who we think is the best in the world, but they also have good players they think are among the best in the world.
"If Leo is ready then he'll play, if he's not then he won't. But I don't think that changes who the favourite is. If he's fit he'll be in the squad and if he's not then he won't be.
"As for the effect he has, it's not for me to answer, it's one for our opponents. But we all know what kind of player he is, what he does for our team and our fans.
"We treat every player exactly the same, some players are declared fit at the last moment and we will react exactly the same to Leo Messi as with any other player in the squad.
Ernesto Valverde: "It's a special game. It's a semi-final and playing against Madrid is another incentive to reach the final"
#ElClásico #CopaBarça pic.twitter.com/59bMaOtCOZ
— FC Barcelona (@FCBarcelona) February 5, 2019
"Ultimately it is down to the manager to make the decision after speaking to the player, the doctors and comparing it to previous injuries.
"Generally we still play the same way, Leo didn't play in the league against them either. If he is [fit] then so much the better but we will try to control the game, stop them from counter-attacking, create our own chances, all the same things as always.
"I like to take risks when you have a cushion to fall back on. If it was the last game of the league it would be a different question. But you wouldn't risk a player with an injury under any circumstances, Messi or anyone. Players with an injury are playing with the handbrake on."
Samuel Umtiti (knee) will miss the game but Barcelona could welcome back the defender's France team-mate Ousmane Dembele from a hamstring injury.
"I can't help you with Umtiti, we're waiting to see when he can rejoin us," Valverde added. "Percentage for Dembele, I can't say until after this training session.
"He worked separately yesterday but will train with the group today, we'll see how he goes, he could be in the squad. The idea was for him to be ready at some point this week, but we have to wait and see."
Jasper Cillessen has played throughout Barca's run to the semi-finals, but a calf injury has ruled the Netherlands goalkeeper out.
"The day of his injury he was pretty upset, he was excited to play against Real Madrid and in the cup semi-final and he won't be able to play," Valverde added.
"I spoke to him the other day and he's accepted the situation, he has to recover. It's a shame he can't play as he's important for us and he has been showing exceptional form. But muscle problems can hit you when you don't expect them, it's very unfortunate."