Mullen limped off in the fifth minute of Saturday's win against Canberra.

The club fears he might have torn the syndesmosis in his lower left leg, which could sideline him for a large chunk of Newcastle's seven remaining regular-season games.

"It doesn't look good, but who knows," a downcast Mullen said after the game.

"I've got to get scans on Monday, but hopefully nothing too bad shows up.

"They think it's torn ligaments, but we're not sure at this stage . . . if it's a torn syndesmosis, it'll be a few weeks on the sidelines maybe six to eight but hopefully it's not that bad."

Mullen said he heard a crack when he was tackled by Alan Tongue.

"My whole foot went numb when I did it I thought I might have broken it to start off with," he said.

The 22-year-old described the injury as "just one of those freak accidents" but admitted it was another frustrating setback.

This season he has broken a rib and dislocated a shoulder yet still played in 15 of Newcastle's 16 games, often under duress.

"I feel like I've killed a Chinaman, the amount of injuries I've had," he said. "I've had a pretty good run this year and only missed one game. Hopefully, fingers crossed, I can come back after the bye, but who knows?"