The Storm gun will be assessed on Monday after coming from the field unassisted in the second half of Saturday's 30-10 win over Newcastle at Albury Sportsground.

The 23-year-old went in to make a tackle but caught a blow to the knee and came from the field soon after.

Scans will confirm the extent of the injury on Monday with coach Craig Bellamy bracing to lose the young star for three or four weeks.

"I doubt if he's going to be ready for round one. It might be three or four weeks, which medials usually are," Bellamy said.

"We'll have to scan him and we'll see how he progresses in the next 10 days."

The Storm are due to open the NRL season with their first match at AAMI Park in a year when they play South Sydney on March 11.

It's a cruel blow for Grant who battled a knee injury while playing for Wests Tigers last year and has struggled to overcome rib and calf injuries this pre-season.

"He's down a little bit, he's had a few injuries through pre-season and we're looking to getting a bit of continuity with his training and playing," Bellamy said.

"He had a couple of things, a rib injury, sternum, and didn't do a lot of contact but that's fine now.

"He had a calf strain at one stage.

"He's struggling to get going with injury on injury, but hopefully he'll get through this and be in the clear."

Grant's latest hurdle could open the door for New Zealand Test hooker Brandon Smith to don the No.9 jersey in round one against the Rabbitohs.

It comes as the two battle it out to replace former skipper Cameron Smith as the club's main No.9 from this season.

"He's a handy player, he can play in the ruck as well and does just as good of a job there," Bellamy said of Smith.

"He adds a lot of energy into our team.

"I'm sure he'll do a good job if he gets that opportunity."

Australian Associated Press