The thing with Kolarov is, he's brilliant going forward whilst also being quite a good defender. We've always seen his attacking play (his overlap with Nasri to setup Agueros first in the 4-1 derby) but he lacks the discipline and raw defensive ability to be able to defend the left-side alone against both winger and full-back. Don't get me wrong he's a very good defender but to be able to defend alone against 2 wide players, as he so often did as Silva gave no defensive cover, you have to be world-class defensively and that limits you going forward. The introduction of Sterling has not only taken Kolarovs attacking play to the next level but the fact Raheem tracks back has shown Kolarov for what he is, a very astute defender who was all too often overwhelmed in formations of past. I love the man