I can see it being Fabinho, Gini and Henderson in midfield in the first-leg, although I think Milner has a very good chance of starting too.
I'd be extremely surprised if Keita starts but if he does, it means he's shown enough in training and in the game against Huddersfield for Klopp to think that he'll be able to disrupt Barca's play defensively.
Big game for Trent and Matip too. A lot of how the game will go will depend on how they deal with Barca getting at them. Matip has been good so far, but there's always a feeling there could be a wobble there somewhere, Trent at times too.
Think it'll be a low scoring match, 1-0 to either side.