"Diomansy has twisted his ankle ligaments and he has got a bit of swelling there," Robson said.
"It should settle down over the next couple of days but I think he'll be doubtful for the Charlton game.
"I was pleased for him before he got injured. Early on in the game he really put Bradford on the back foot and got himself a goal.
"It was a bit unfortunate that we could not see a bit more of him because of the injury."