I'd start one of the Fern's alongside Delph and replace them at half time with the other.
I'm surprised everybody has picked Navas. He's started thirteen games on the bounce. Has anybody else played that many? I'd be starting Sterling in his place, as it's vital he gets a decent number of minutes under his belt before Wednesday's game. Was quite surprised he didn't play any part at all against Stoke.
Would start Kelechi in place of Aguero too. He'll be flying after last week.
Full backs will both probably be rotated, but do we need to rest both? Both Sagna and Clichy have had time out recently.
If Toure and Nasri are fit, I'd go with:
Hart, Zabaleta, Otamendi, Mangala, Kolarov, Delph, Fernando, Sterling, Toure, Nasri, Kelechi
Subs: Caballero, Demichelis, Clichy, Navas, Fernandinho, De Bruyne, Aguero
If Yaya and Nasri aren't fit, I'd be looking at picking De Bruyne and possibly Manu Garcia or Celina in their places. As good as Southampton are there could be worse places to make your first PL start.
In terms of the debate as to which game should be prioritized, I'd have to say Wednesday's. The big aim of the club is to win the game's biggest prizes and obviously triumphing on Wednesday puts us very close to that. If we didn't get top 4, but lost out on it because we prioritized a CL semi final, then it would still be a blow, but easier to take.
As for a prediction, I reckon this will be a draw.