Some quarters had suggested that the big American was set for a lengthy spell on the sidelines but thankfully no ligament damage has been sustained so the former Colorado Rapids man has returned to training in preparation for Saturday's game.
The USA international sustained the injury during stoppage time whilst making a remarkable save from Rotherham's John Mullins at point blank range.
Speaking to icberkshire.co.uk, Hahnemann confirmed that he is ready and able to play on Saturday.
"I jarred my knee making that save at the end. It swelled up a bit and was painful but thankfully there's no ligament damage and is just a bit of bruising.
"I trained lightly on Wednesday and by taking it easy I haven't had a problem. With a couple more days before the Wimbledon game, I'll definitely be fine to play."
Reading are hoping to avenge last season's two embarrassing defeats at the hands of the Dons. The Royals were unlucky to be beaten 1-0 at the Madejski Stadium last year but were comfortably dismissed by two goals to nil in the return fixture at Selhurst Park.