March 20 (Reuters) - Manchester United ( MANU ) manager Michael Carrick says Matthijs de Ligt's recovery from a back injury is progressing slower than expected and he has no idea when the Dutch defender will be able to return to action.

De Ligt, 26, has been sidelined since United's 2-1 win over Crystal Palace in November and there are doubts he will be fit for the World Cup, which starts on June 11 in North America. "It's one of those things with backs that, sometimes, you think it's alright and then, all of a sudden, it's not quite right," Carrick told reporters on Thursday.

"We'll obviously give him time and try to get him back as quickly as we can. But it's really difficult to say. I am not trying to hide anything.

"Literally, at the moment, we don't know, so we'll have to wait and see."

Manchester United ( MANU ) are third in the Premier League and face Bournemouth later on Friday. (Reporting by Karan Prashant Saxena in Bengaluru; Editing by Peter Rutherford )