If he isnt 100%, i sure hope not, this game is lost before its even played, no point taking any risks.
This doom and gloom attitude seems apt, but strange things happen in football. Almost nothing here is in our favour, from form, to backroom politics. In these circumstances results actually tend to be opposite of what is expected.
Playing Marcelo would be the same decision as Simeone playing Costa in 13/14 final. Can backfire, but this is pretty key for the manager and the team. You can't bench a player like him if he has a chance to feature. It's not like we're risking the rest of the season under this manager and with this squad, who was only barely expected to go for the league title only. Lopetegui has to play his best lineup or he accelerates his sacking, which is 95% done. Not letting Marcelo play would be sensible, but the comms aren't perfect between the two, Marcelo had come off injured in September after the final sub was made already and there also was this episode where he got subbed and Marcelo voiced how 'he didn't understand it but respected it'. So basically either Lopetegui puts his foot down and benches him, but that would mean playing a conservative lineup in a game he needs to try to win, or he lets him out there given Marcelo will probably not admit to not being fully fit.
In any case, he will almost surely play. I didn't see the tackle against Plzen, but saw a photo so if that was an impact related thing and it's not muscular, then there's no reason to think he'll be at risk of reinjuring himself.
Edit: Lopetegui pretty much confirmed on the conference it was only a bruise, he's training normally and seems able to play.