Lionel Messi will miss Barcelona's trip to Getafe on Saturday after tests on Wednesday confirmed he has a thigh strain.
Barca have not revealed how long he will be sidelined for but sources have told ESPN FC that he's expected to be out for between seven and 10 days, making him a major doubt for upcoming games against Inter Milan and Sevilla as well.
Defending Spanish champions Barca are looking for their first away win of the season.
Messi, 32, made his first start of the campaign in Tuesday's 2-1 win over Villarreal at Camp Nou but he was forced off with a groin problem at halftime.
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He underwent tests on Wednesday as club doctors confirmed the strain. The Champions League group stage against Inter Milan and then the league match with Sevilla follow Getafe before October's international break.
Coach Ernesto Valverde downplayed the severity of the knock, and said he was taken off as a precaution, but he is likely to be without his forward for this weekend's game in Madrid.
Barca have dropped points at Getafe in two of their last four visits and are without an away win in four games in all competitions this season following Saturday's loss at Granada.
Messi had only just returned to action after missing the first four games of the season with a calf injury. He made his comeback off the bench against Borussia Dortmund last Tuesday.
Barca didn't rush him back from that injury for fear of a relapse and sources have told ESPN FC they will adopt the same stance with the groin problem.
Speaking in Milan after winning FIFA's The Best on Monday, Messi said he didn't feel at his best in the game at Granada after coming on as a substitute at half time.
"It had been two, nearly three months without playing and you could tell," he said. "I felt tired and sluggish. I didn't have that spark. I was lacking a bit of rhythm."
With Messi missing, extra emphasis will fall on Luis Suarez, but the Uruguay international striker has been struggling for form.
Suarez scored twice off the bench against Valencia but has blanked in his last three appearances and was whistled by sections of the Camp Nou crowd against Villarreal when he was replaced by Ansu Fati.
"I understand the fans have their opinion on Suarez, they pay for their tickets and can say if we are not doing well, but players are people, too," defender Gerard Pique told reporters after the Villarreal win.
"We can't be 100% in every game. I wouldn't give too much importance to the whistles."