Messi out for at least two matches
Tests confirmed ligament damage to the Argentina forward's right ankle and he will be unavailable for the home game against Sporting Gijon on Wednesday and Saturday's trip to Athletic Bilbao, Barca said on their website.
Messi was taken off on a stretcher in added time at the Calderon after he was felled by a bad tackle from Czech defender Tomas Ujfalusi.
Ujfalusi was shown a straight red for the challenge, which has revived debate in Spain about whether players like Messi and Real Madrid's Cristiano Ronaldo need special protection from referees.
Messi's participation in Barca's Champions League match at Rubin Kazan on September 29 will depend on his recovery, Barca said.
The test carried out on Monday also confirmed there was no damage to the bone.