Yeah I'm worried about a back up GK.I'm sure you can get much better goalkeepers on the free agent market every year than Pena.
With salary cap issues though, I guess Pena is on really low wages and won't complain about not playing. But we're talking about a LaLiga winning, CL contender club here. If Stegen goes down then so does our whole season. And we can't keep running that risk with guys like Pena as backup goalkeeper.