Diop then came off the bench and made the winning goal for Brian McBride.
"I was in my office and I found out before the game that Antti Niemi had landed funny and pulled a muscle in his back, which is disappointing news," Coleman said after the 2-1 win at The Cottage.
"So then Papa Bouba Diop gets a chance on the bench. That's football, isn't it? He only came on because Moritz Volz had had two or three heavy collisions and I think with another one we might have lost him.
"I knew Bouba was ready to come on and prove a point. He came on and did terrific, he made the second goal for us.
"But more importantly his all-round performance was good and that's more like it from Bouba. We had a lot of phone calls for him and loan deals, but that's not something we're interested in.
"It's common knowledge he talked with Wigan, but he wanted to stay with us and prove a point. When he's on song he's a force, but he's got to get back to his best."