Griezmann played the first half in the 1–0 victory away, but was replaced by Luis Suárez after the break.
A more thorough examination on Sunday showed that he had badly damaged the front of the right thigh.
"The development of the injury will determine when he is back," Barcelona writes.
The Catalans have a point up to Real Madrid in La Liga with a match more played. Two rounds remain of the season.
More La Liga: Barcelona kicked out Espanyol (July 9, 2020)
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Barca kicked out Espanyol from La Liga Photo: Photo Agency