I'd rather have Griezmamn as back up for Suarez that's if the flanks are occupied already, but with Dembèlè proving to be unreliable, numerous back up plans wouldn't be a terrible idea.
Griezmann has a too much quality to be a back up striker. He would have to be featured regularly one way or the other. Valverde has shown interest in 4-4-2 formation, and Griezmann can function behind a centre forward.
Dembele's injury is a big blow, as he is really the only first team player who can use both feets available now in the attack. Barcelona would have a hard time filling up the left flank of the attack.