Elliott was forced off after just 12 minutes in the 32-26 victory against Bristol after dislocating his shoulder and has required surgery.
That means the 24-year-old will spend another spell on the sidelines, having previously been out until November with another shoulder problem.
And Mallinder said: “It’s bad luck for him and he’d already had a previous shoulder injury, but he’s patient and everyone will wish him all the best.
“He’ll come back a better player.”
But there is better news for Saints in the pack, with Calum Clark, who has not required surgery on his knee injury, and Sam Dickinson making good progress.
“Calum’s improving, as is Sam Dickinson, so two back rowers there who have both been out with leg injuries but who are making good progress,” Mallinder said.
“Sam Dickinson will probably be back sooner than Calum Clark.
“With Louis Picamoles going (to play for France in the Six Nations), Tom Wood very likely (to be with England) and a possibility of Teimana Harrison as well, back row is an area where there will be opportunities.
“We’re fortunate that we’ve got the two we’ve just mentioned coming back, but also people like Ben Nutley and Lewis Ludlam, who are two great players and who we are looking forward to seeing play more.”