Dembele underwent surgery on his hamstring in February and has not played a competitive game since November while Griezmann missed the end of the LaLiga season with a thigh problem.
Dembele has been heavily linked with a move away from Barca after suffering multiple injuries since joining the club from Borussia Dortmund in 2017.
Griezmann has had a frustrating first season after joining from Atletico Madrid with the 29-year-old only managing nine goals in the league, six short of his tally for the 2018-2019 campaign.
Barca will host the second leg of their last-16 Champions League tie with Napoli at the Nou Camp on August 8. The scores are locked at 1-1.