Midfield alternatives are Frenkie, Rakitic, Riqui and Roberto. Now Roberto will start for sure, the question is as a CM or as RB.
If Roberto plays in midfield I think Riqui (wrongly) will be sacrificed.
Roberto and Frenkie offer the same qualities as CM's with Frenkie being better, so I'd personally start Rakitic as DM with Riqui and Frenkie in front.
Up front I can't see any other alternative than Griezmann, Suarez and Messi, either in a flat line or with Messi behind them.
I think Setien will opt for the latter, which with a bit of fluidity will look like:
Suarez
Roberto/Riqui, Messi, Griezmann
Rakitic, Frenkie
Alba, Lenglet, Pique, Semedo/Roberto