Speaking at a press conference to preview our Premier League home game with Fulham, head coach Michael Carrick was asked to confirm reports that the 21-year-old will be out for a number of weeks.
"Pat is going to be out for a period of time," he said. "We're still working through how long that's going to be.
"He's had such a good couple of weeks and we weren't sure if it was cramp or something more serious, but it looks more serious.
"Whether it's a few weeks or more, we're going to have to wait and see.
"Unfortunately, it's something you have to work through in football."