Speaking in his press conference, which was held before training, Valverde refused to speculate on whether the Argentine would play or not. "If he is fit, he will play and if he is not, he will not play".
"It is true that sometimes we have had doubts with players and we have waited until the last moment", he said.
Barca face a testing period of fixtures, including three Clasicos in the next month.
Keylor Navas of Real Madrid during the Copa del Rey second leg Quarter Final match between Girona FC and Real Madrid at Montilivi Stadium on January 31, 2019 in Girona, Spain.
Valverde indicated he would be cautious with Messi's fitness.
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Here, we take a look at the major talking points ahead of the game.
"If it was the last match tomorrow, than it would be different", he said.
Santiago Solari will be looking to become only the first Barcelona or Real Madrid manager in the 21st century to win his first El Clasico in the dugout, next to Zinedine Zidane. There is no favorite in a semi-final between Barca and Madrid, it is an open game, we have great players and among them is the man we think is the best player in the world.
Ousmane Dembele, who also trained after recovering from two weeks out with an ankle sprain, has not been named in the squad.
Asked whether Vinicius' recent displays made him undroppable, Solari replied more shortly that: "Nobody is undroppable in football". We'll make a decision based on that. "The calendar is very complicated", he said. Despite those results, though, Madrid are still eight points behind Ernesto Valverde's side in the league. They appear a team transformed since the 5-1 defeat by Barca in October. Vinicius plays better at the Bernabeu.