Hull City striker Will Keane has been ruled out for 12 months with knee ligament damage.
The 23 year old former Manchester United player suffered the injury in the 2-1 win over Southampton on 6 November and will have surgery on Tuesday.
"To lose a player of Will's quality and potential for such a long period of time is a big blow," Phelan told the club website.
"I'm sure his determination and mindset will see him through the tough journey ahead."