Foster, who was speaking about Chelsea as part of the, insisted that Courtois' lack of quality when it comes to playing with his feet would have hindered him under Sarri.
"When it comes to Courtois, brilliant with his hands, but, really, actually, quite crappy with his feet," Foster said.
"They (Chelsea) didn't force him to play a lot. Whereas Sarri wants him to do more of a Man City job. You keep the ball. People come at you don’t stress. Be calm, play triangles. Let’s play around our box here; three, four, five passes. The objective is not to get it as quickly as possible.
"So that’s why Kepa is actually a good signing. That’s why I think, provided he deals with the initial moments of the EPL and he can adapt quickly. He actually may end up being a much more appropriate goalkeeper for what Sarri likes to do."