Closer to home, Manchester City manager Stuart Pearce has not ruled out trying to set up a deal with the player.
"I think this club would like to be associated with good players and Roy Keane falls into that category," said Pearce, who spent three years with Keane at Nottingham Forest in the early 1990s.
"Every club in the world at the moment has their name attached to Roy Keane. I think the fact we are in a city where he lives and works means we might be attached as well."
Portsmouth were one of the first Premiership clubs to declare an interest in Keane, while Wigan, Everton, West Brom and Aston Villa have all been linked to the player.
Meanwhile, Birmingham manager Steve Bruce, who played alongside Keane at United in the early 1990s, ruled out making any attempt to bring the Irishman to St Andrews.
Bruce said: "I think he has still got something left as a player. I know him well. I wouldn't be surprised if something is already sorted. Will we be trying to sign him? No, I think we can rule that one out, that's for sure."
A move to Celtic also seems to be on hold.
Chief executive Brian Quinn has said Keane would need to take a severe cut in wages if he was to go to Parkhead.
"There are two separate issues," Quinn said.
"One is a footballing issue, whether Roy would fit into Gordon's plans and the formation - because the team is playing very well just now and is very settled.
"But that is Gordon's judgement and we have to take that into account. The other is the business side, and we would have to wait and see what is proposed.
"We have heard nothing from Roy Keane, nothing from his representatives and until you see what the proposal is, it is premature to offer a view on that."