Paul Gallen has declared he will be "100 per cent fit" for Cronulla's NRL preliminary final against North Queensland on Friday night.

Gallen missed the Sharks' qualifying final victory over Canberra with a back injury a fortnight ago, and has at times struggled to get out of his car or bed since pulling up lame from a regular training session before the match.

And while coach Shane Flanagan cleared him on Sunday to return for the must-win grand final qualifier, Gallen has confirmed he won't carry any injury concerns into the match.

"If nothing goes wrong between now and the game I will be 100 per cent fit," he told Sky Sports Radio's Big Sports Breakfast.