Dunn was taken to hospital after being injured early in the game making a brave block from Bury's Damien Mozika in an accidental collision and may be out for several games.
Manager Gary Johnson said: "Chris had 14 stitches on Saturday afternoon and now has a very bad black eye.
"However, it could have been worse so we are at least thankful that it wasn't.
"It was a brave save from Chris and that is what you need from your keeper and it is unfortunate that he sustained the nasty injury that he did.
"Our thoughts go out to him and he will be working with our medical team and facial injury specialists to hopefully be back in action as soon as possible in the next few weeks."
Source: PA
Source: PA