David Ribbans is set to miss Saints' clash with Lyon on Saturday afternoon.
The lock suffered an ankle injury in the win against Benetton last Sunday and was in a surgical boot after the game.
Saints are still awaiting news on how long Ribbans will be sidelined for, but they are more positive on George Furbank and Courtney Lawes.
Furbank tweaked a groin problem, while Lawes was battling illness.
But both look set to be able to be involved at the Matmut Stadium as Saints go in search of a win that would really enhance their chances of making the Champions Cup last eight.
"Sometimes you have to wait with various injuries for the player to get scanned," said Saints forwards coach Phil Dowson when asked for a midweek update on Ribbans.
"It's one of those where we're desperate to know what the situation is but you're still waiting for reports and they can't scan it because of the swelling.
"We're still waiting on the medical stuff and it's unlikely he'll be involved this week.
"He's frustrated because he wanted to play last Sunday and he didn't get many minutes.
"We're hopeful he won't be out for too long, but we don't really know what's going on."
On Furbank, who had to pull out just before kick-off last weekend, Dowson said: "It wasn't worth risking.
"He'll get treatment this week and the front end of the week will be quite light with him building up the load to make sure he's 100 per cent for France."
And on Lawes, he said: "He was touch and go whether he would start and he made it to half-time, but hopefully he'll have a full battery recharged and be ready to go on Saturday."
Piers Francis and Matt Proctor have both been battling concussion, which forced both centres to miss the clash with Benetton.
And Dowson said: "They're going through all the protocols.
"They've trained, they're in amongst it and they've done various things like the bike, running, doctor tests so they're on the way back.
"When we've got guys like Fraser (Dingwall), Hutch (Rory Hutchinson) and Simmo (Andy Symons) playing so well, we don't want to rush them back from concussion issues."
Jamie Gibson remains sidelined with a broken ankle, but Alex Mitchell is increasing his training load as he looks to make a return from a long-term knee injury in the near future.
"I've seen him running around," Dowson said of the talented young scrum-half.
"I've seen him doing some passing with Sam (Vesty), he's done some box-kicking stuff and he's taking a part in training a lot more.
"He hasn't done a huge amount of contact as yet - as you can imagine, it's a slow process build-up.
"You do running, straight-line running, off-line running and then that chaotic running where you have to step and move.
"He's been playing games and stuff but as yet I don't think he's done contact, but that's imminent.
"He's a player we're very excited about and we don't want to rush him."