Mitch Eadie is set to miss the next few weeks after suffering an ankle sprain in last Saturday's defeat to Saracens at Twickenham.
No.8 Eadie, who moved to Northampton from Bristol during the summer, was forced off just 15 minutes into his competitive debut for the club.
He received lengthy treatment on the pitch and was later sent to a specialist to undergo a scan.
But Saints attack coach Alan Dickens says the news is more positive than first feared.
"He's been to see the specialist this week, had a scan and it's pretty positive," Dickens said.
"Obviously he got a really nasty injury and had to come off, but the diagnosis is more positive than we thought.
"It's a high ankle sprain.
"It was disappointing for us because he was excellent in pre-season. You go back to the game against Ulster here and he was really effective."
Saints could now look to select Teimana Harrison at No.8 for Saturday's game against Leicester Tigers at Franklin's Gardens.
Harrison played no part in last weekend's opening-day loss, but is fit and available should Saints choose to select him against Tigers.
"Mitch Eadie, Stephen Myler (knee) and Piers Francis (jaw) are the only ones missing," Dickens said.
"Teimana is available and we've got a fully fit squad apart from those three I've mentioned."