A BROKEN thumb will sideline Carlton forward Brad Fisher for up to two months.

The Blues said Fisher had a pin inserted to the base of his thumb on Monday, after sustaining the break during Saturday's match against Port Adelaide.

The 23-year-old is expected to be out for six to eight weeks, which means he could miss up to four matches of the home and away season.

Fisher's loss is a major blow to the Blues, as he was the club's second-highest goal scorer last season, behind Coleman medallist Brendan Fevola.