Messi, the all-time top-scorer in Spanish football as well as in the "Clasico", ended Barca's 2-2 draw with Valencia on Saturday with a knock.
Lionel Messi has scored 12 goals in his last nine games.
Speaking ahead of the match, Barca boss Ernesto Valverde, hinted he will strill carry out last minute check on Messi before making his decisions to play him. "We'll see if he can complete the session, if he will show that he is in condition to play".
There was good news for Barca fans Tuesday.
The Argentine forward was impressive for the Catalans in their dramatic 2-2 comeback against Valencia over the weekend.
He was rested two weeks ago when Barcelona lost at Sevilla 2-0 in the Copa quarterfinal first leg, but returned to score in a 6-1 second leg victory. "Neither are strong defensively and, with Messi largely excused from playing in his own half, fielding Dembele and Coutinho together is a risk that conservative coach Valverde is reluctant to take".
"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.
"I don't think it changes anything", he added when asked how a hypothetical Messi absence could influence proceedings.
Valverde admitted he might have to rotate his line-up given the number of important games coming up.
The former Madrid player and Castilla youth team coach was happier to go along with local reporters who suggested that La Liga's authorities had favoured Barca by giving them an extra day to prepare for both Wednesday's first leg and the return at the Bernabeu on February 27. "We are in a decisive part of the season".
Real Madrid also have the small matter of the Madrid derby not to mention Champions League fixtures against Ajax in a hectic schedule. "We are expecting them at their best".