Wigan Athletic star faces devastating season KO
But his first start for Latics - a man-of-the-match showing at Ewood Park - may also be his last after boss Shaun Maloney's worst fears were realised.
"It's tough news for Martin," said the Latics manager. "It's a serious knee injury, and unfortunately Martin's season is over on the pitch.
"It's devastating for him and for us, but he'll still continue to be a big part for us on the pitch.
"He was everything I could have wished for and more in terms of a new signing coming in.
"Martin was the quiet leader off the pitch, but on the pitch he became a monster which we saw at Blackburn.
"He'll be a big miss but he still has a big part to play."
Fellow January recruit Omar Rekik - who joined on loan from Arsenal for the rest of the season - also pulled up lame at Blackburn with a muscle injury, although that is nowhere near as serious.
"We're not sure about him, but he's a big doubt for the weekend," added Maloney.
"As with any player, I'll give them until the last session, the last day, to prove they're fit to play."
Latics have scope to bring in a free agent after only naming 24 players in the squad they submitted to the EFL earlier this week.
Maloney, though, played down talk of an imminent arrival.
"We haven't thought about the free agent market," he said.
"My view is that we will continue to improve the players we have here, and we'll go with that.
"Especially in that defensive line, there's improvement individually and collectively to be had."
Centre-back Jason Kerr has already been ruled out for the rest of the campaign after suffering his own serious knee injury at Swansea back in November.
Charlie Hughes and Curtis Tilt look like being the two most likely to come in for Kelly, after being left out of the squad on Monday night.