Porto is playing with almost an entire team of substitutes for this leg. It makes sense as a bunch of the main 11 is injured and the manager wants to rest the remaining top players for the real objective: the portuguese league. Only Felipe, Casillas (went back to the main 11 after the aweful exibition in the first leg of the young goalkeeper Sá) and Aboubakar (just recovered from a 1 month injury so he's not at top form) are part of the main 11.
I am curious to see how Dalot will perform (extremely promissing 18 year old right/left back from Porto B) and Bruno Costa as well (another youngling from Porto B). Liverpool will probably slam this Porto B "per se", but at least a few players will gain champions league experience.