The former Blackburn Rovers striker has returned to England from Olympiakos despite enjoying a good reputation with the Greek club's supporters and the prospect of Champions League football this season.
"I've been very impressed by what I've heard from Steve McClaren. He has got massive ambitions for the club. I want to be a part of that," said the 25-year-old. "You don't become the England manager if you are not a good coach and I'm looking forward to working with him.
"I also know (assistant manager) Rob Kelly as he was the coach who took me to Blackburn when I was a youngster and I believe that, as a player, I'm only going to benefit from working with them."
Forest meanwhile will travel to face Wycombe Wanderers in the next round of the League Cup.