The first thing Zabba did, when he came on, was get skinned alive & hack down the oppo player. I'm glad he wasn't on from the start.
Imo Fernadinho did absolutely fine, for a new player starting at fullback & far better than Zabba did when he started there. And the surprising thing was that it was his passing choices which were the weakest part of his game, not his defending.
Perhaps some people think Zabba 7 Sagna are actually better footballers than Fernandinho, & therefore have an advantage. I'd say they can't lace his boots, so therefore, if Pep requires it, Fernandinho can learn the right back position, far quicker than Zabaleta did.