Darren Bent insisted he had to leave Aston Villa after too many "slaps in the face".
Brighton defender Greg Halford has agreed to extend his loan deal from Nottingham Forest until the New Year.
The 20-year-old is set to join his United colleague Nick Powell at the DW Stadium, although the deal may not materialise until next week because Keane picked up a knock while training with the England Under-21s last week.
Keane, whose twin brother Michael is also at Old Trafford, suffered a cruciate knee ligament injury in the early part of 2012 and missed 16 months as a result so Coyle is keen to err on the side of caution when it comes to any knocks now.
"Will Keane is a player I've admired for many years. He's a young lad who has continued to progress at Manchester United," said Coyle.
"We have a verbal agreement with Manchester United regarding Will Keane. He'd been away with the Under-21s and took just a slight knock. I spoke to David (Moyes) last night (Wednesday) and given the lad had a very serious injury, we will always be guided by Manchester United in terms of when he feels the right time is for the lad to come in on loan. That's where we are.
"I think with regards to this week that will probably be too soon but hopefully he recovers from that and if the medical team at Manchester United are happy with it then there's a possibility we could have that done for next week.
"It will be brilliant to bring him in because I think this is a lad who is going to be a top player. He certainly knows where the goal is but more than that he's a real team player. He plays beyond his years in terms of his knowledge of the game and it will be great to have someone of that quality in the squad."