I doubt Jung would be happy to sit on the bench for 2 years waiting for Sagna's legs to go. Would make absolutely no sense in signing a RB if we keep Bac.
To be honest, i'd much rather us sign a LB, Gibbs is injury prone and unreliable, Monreal has become awful, makes more sense to strengthen a weakness, rather than weaken a strength.
Jung isn't going to sit on the bench for two years. Sagna, if we do extend his contract is not going to make it as first choice for another year. He isn't close to being the player he was 2 or 3 years ago. You very rarely see him getting round the back of the defense any more, and he is a lot slower coming out to the winger on his side. Still a good player, and a good back up CB, but by the end of next season, he will be a back up RB, if we are up there challenging where we want to be.
He is in the same situation as Arteta was last year. Very experienced, he's had a good season, but you can tell that the years are catching up.



