The pair skipped Melbourne's training run before their AAMI Park clash on Saturday night, rested following Wednesday night's torrid encounter when their Queensland side suffered a last-ditch defeat.
Forward Trent Loiero took part in the session after only coming off the Maroons bench for 14 minutes near the end of the match.
The Roosters also have six Origin representatives, led by try-scoring hero James Tedesco and hard-working halfback Sam Walker, named to play.
"Whether they play or not, I'm not quite sure yet, but we'll just see how they pull up, tomorrow, but they won't be doing any training," Bellamy said of Munster and Grant.
"They'd like to play, yeah, but, whether it's best for them or not, we're not quite sure yet - they need to have a few more checks and then go from there."
Munster was spotted in Storm training gear and told AAP he'd done a light run-through, signalling his intention to play.
With Melbourne languishing in 15th spot with just four wins for the season and taking on the Roosters, who are third, the Storm can ill afford to have two key men on the sidelines for the round-13 clash.
They have utility Tyran Wishart sidelined with an ankle injury and can no longer call on the likes of their usual Origin cover with Jonah Pezet and Bronson Garlick both having left the club.
The Storm snapped a record seven-game losing streak but their second-half woes resurfaced when they were over-run by Canterbury last round.
Bellamy admitted their faltering form had made it a "confusing" time in his long, decorated coaching career.
"We've already tried to tweak a few things and there's only so many things you can tweak," he said.
"I can't remember the last time in my coaching career that I've been as confused about, that - we've tried a few things, different things, and we just can't seem to get that right in the second half.
"I'm pretty set on what we need to do now, but for a couple of weeks there it was a bit confusing."
He said the depth of the Roosters talent made them difficult opposition even if their Origin players didn't make the trip to Melbourne.
"They're a really good side, they've got a lot of talented players in there - there's probably another four or five players that could have played Origin as well so they're a classy side.
'They're a really good club, always have been, and just hopefully we can get our game on tomorrow night."
