Andres Iniesta has been ruled out of Barcelona's league game at Eibar on Sunday with a calf injury, the club have confirmed.
Iniesta underwent tests at the club's training ground on Friday after being substituted during the 1-0 Copa del Rey quarterfinal first leg win over Real Sociedad on Thursday.
The midfielder was replaced by Andre Gomes at half time after complaining of a light pain, but Barcelona are hopeful he will return for the second leg at Camp Nou next week.
"Tests have confirmed that Iniesta has a calf problem and will have to sit out Sunday's game against Eibar," a club statement said.
"Club doctors will need to monitor the captain's progress before determining his availability for other matches."
Iniesta missed six weeks with a knee injury earlier in the season, returning as a second half substitute in December's draw with Real Madrid.
Barca suffered a slump in results without him, drawing four out of five games at one point, while his return to action prompted a five-match winning streak.
Rafinha is the only other Barca player missing through injury for Eibar, with a hamstring problem having kept him out of Thursday's game.
Andre Gomes, Ivan Rakitic and Denis Suarez are Luis Enrique's other midfield options for the two places in front of Sergio Busquets.
Last weekend's win against Las Palmas, coupled with Real Madrid's defeat to Sevilla, has allowed Luis Enrique's side to move to within two points of the leaders.