Bill Murray used to think Miley Cyrus was a ''knucklehead'' - but is now a fan.

The 64-year-old actor - who stars in new comedy movie 'Rock the Kasbah' alongside Bruce Willis and Kate Hudson - has revealed he's grown to admire the 'Wrecking Ball' singer, who he described as a ''pro''.

Bill said: ''I'm gonna say this officially: Miley Cyrus is good.

''I thought she was a knucklehead, funny girl. But she can really sing and she floored everybody. I don't want to hear any more bad rap for Miley Cyrus. Not Miley Cyrus. She's a pro.''

However, the popular actor was less complimentary about American rap star Rick Ross, who he's recorded a Christmas show alongside.

Bill joked: ''We'll leave [the bad rap] for Rick Ross.''

In March, Bill called on the public to let him know the whereabouts of the rapper after he failed to show up to a planned meeting.

He explained: ''We're doing a Christmas show and my friend is friends with him so thought he would be great to sing this one song. So he came and recorded the song and ... that was the last we saw of him.

''He didn't show up to shoot it. If anyone out there sees a 300lb guy who looks like he's supposed to be in New York two weeks ago let me know.

''It was a lot of fun, he just got lost. I kept saying, 'He better be dead, otherwise he's in trouble.' ''