Nik Kosef (born 6 June 1974) is an Australian former professional rugby league footballer who played as a lock, five-eighth and second-row forward in the 1990s and 2000s.
Kosef made his first-grade debut for Manly in a round 18 match of 1992 against the Penrith Panthers.
He played for the club and its related successor the Northern Eagles for eleven consecutive seasons although his last three years were interrupted by injury.
He was a member of Manly's premiership winning side of season 1996 as well as the teams which lost the Grand Finals in 1995 and 1997 to Canterbury and Newcastle respectively.
[citation needed] Kosef made his return to the team in 2002 after sorting out a contract dispute with the club.