The Chilean attacker reportedly suffered a minor knock in the Blaugrana's recent match at Stamford Bridge and his availability for the crunch game against Los Blancos is in doubt
The Chile international came off in the second half of his side's 1-0 defeat to Chelsea in the first leg of their Champions League semi-final tie.
Upon returning to Barcelona from the match in England, Alexis was still seen limping, reportedly from a harsh challenge from John Terry during the second period of the match.
It is said that the player will undergo a series of tests on Friday to determine whether he will be available for the crunch game against the capital club.
The former Udinese ace, who joined Barca in the summer for an undisclosed fee, has scored 13 goals in 37 competitive appearances this season.