The Hull KR player, who joined on loan from Huddersfield Giants for the rest of the season in March, has been absent for the last two months.
Hopeful head coach Chris Chester had named improving Lunt in his 19-man squad in each of the last two weeks only to, crucially, see him then fail to be fit for match-day.
He left him out of his initial pick for tonight’s game against Warrington Wolves and said: “Lunty’s going to see a specialist in Leeds at 12 o’clock on Friday.
“Last week he trained really well on the Wednesday and Thursday, then we had the day off but he wasn’t able to run the final session before we played Widnes so we had to pull him again.
“I’ve not named him in the 19 at all this time. It is frustrating, none more so than for Lunty.”
Chester explained: “He has a twisted spine which we’re confident is not a serious and unmanageable problem.
“But this is more for peace of mind to make sure there’s no other damage there.
“Even when he’s sat at home he’s having to lay out on the floor and it takes about 40 minutes of rehab’ before we can get him out on to the training pitch.”
Cumbrian Lunt, 28, had an instant impact for Rovers, scoring two tries on debut in the victory over Catalans Dragons.
After a slow league start, it began a run of four wins from five as the ex-Leeds Rhinos rake highlighted all his experience, creativity and support play.
His last outing, though, was the Challenge Cup win at Bradford Bulls on April 19.
Already without captain Terry Campese, the club are desperate Lunt is fit in time for their Challenge Cup quarter-final with Catalans Dragons next Thursday.