The first leg of the semifinal in the Copa del Rey is the first of three matches between the rivals in less than a month.
The Argentinian missed training on Monday but was back with the squad on Tuesday evening.
Forward Ousmane Dembele is also unlikely to be fit for the first leg at the Nou Camp, as he is still recovering from a hamstring injury.
It's obvious that the team would feel more confident with Leo Messi on the pitch, as well as the home crowd, but he is a doubt for this match, and it seems unclear if he is going to play or not.
"There is still one practice session left, we'll see how he's feeling", Barcelona coach Ernesto Valverde said.
Valverde indicated he would be cautious with Messi's fitness.
Real Madrid coach Santiago Solari said the uncertainty about Messi wasn't affecting his team's preparations.
The Real Madrid manager believes Cristiano Ronaldo is the best player in the world but only because Lionel Messi is playing another sport. "Then you have a decision to make and you have to weigh up the pros and cons". Yes, Valverde rotated his team for previous rounds, but this is a special match that no one wants to lose and is also important to get a good result before the trip to Bernabeu. The French striker has 18 goals, six more than he had in all of last season. "We are in a decisive part of the season".
"In a semifinal between Barca and Madrid there's no favourite".
But the way Barca play allows them to save energy more than other clubs as they have great ball possession and force their opponents to run a lot.
For instance, Roma dealt a huge blow in last year's Champions League when they knocked out Barcelona by defeating them 3-0 in the second leg. Barcelona were ahead by a three-goal margin but their players failed to show up at Rome which ended their hopes of conquering Europe.