"In Leo's case, yes he is fine, he trained normally," Barca coach Gerardo Martino said before the clash between La Liga champions Barca and Copa del Rey winners Atletico.
The return of Messi, who missed Sunday's 1-0 La Liga win at Malaga, raises the prospect of the Argentine World Player of the Year and new signing Neymar starting a competitive match together for the first time.
Martino has been breaking the Brazil forward in gently since he joined from Santos in the close season and he has played only the final half an hour of Barca's three matches this term.
The 21-year-old rescued his team in the Super Cup first leg when he came off the bench to head the equaliser, giving them a slight advantage of an away goal ahead of Wednesday's return.
"He is ready as always and tomorrow we will make the decision," said Martino, who is bidding for his first silverware since taking over last month from the ailing Tito Vilanova.
"It's what I think best taking into consideration his arrival, all the interest he has generated, what he experiences every day," the 50-year-old added.
"To avoid him being overloaded when he is still getting to know where he is playing, the club, the players.
"Barcelona is too big a club to assume such responsibility so quickly and I am trying to create the conditions for him to get used to it in a different way.
"I aim to make him a Barca player for 10-12 years, I don't expect him to solve my problems in a single match."
Wednesday's showdown features two Argentine coaches and Martino's Atletico counterpart and compatriot Diego Simeone said earlier he hoped both Messi and Neymar would feature for the benefit of the spectacle.
"For those of us who like to watch football, hopefully Messi will play, Neymar is also a great entertainer," the former Argentina midfielder, who also played for Atletico, Inter Milan and Lazio, said.
"We're expecting the best of Barcelona. We'll be ready for the best Barcelona," added the 43-year-old.
"They are better than us and have more chances of scoring.
We have to prepare for that. The game lasts 90 minutes and we will look for how we can damage them."
Martino also addressed Barca's close-season search for a centre back. He said the club would probably not buy anyone before the transfer window closes at the start of next month but could sign a defender in the January window if necessary.
Barca were chasing Brazil captain Thiago Silva but he has elected to stay with Ligue 1 side Paris St Germain.
"I consider this the group I want to work with and I have enough," Martino said. "As the season goes by we will see if there is a need for a centre-back."
Barca celebrated the signing ceremony for Sergio Busquets's contract extension on Tuesday, with the Spain midfielder inking an already-announced deal to the end of the 2017-18 campaign with an option for one more season.
Still only 25, Busquets has won four La Ligas and two Champions Leagues with Barca, as well as a host of other titles, and the World Cup and European championship with Spain.
"It's a dream come true being able to continue at the world's best club, which is the club of my life," Busquets said.
"I try to improve every day. I want to win more titles, fight to win each match and put on a show with the same philosophy that we've had up until now."
Barca's promising Spain winger Cristian Tello, who turned 22 this month, will sign his contract extension until the end of the 2017-18 campaign on Friday.