Chris Boyd has confirmed Harry Mallinder suffered a knee injury during Saints' 41-20 defeat to Clermont Auvergne on Saturday.
But the boss says the initial signs are that the problem is not too serious.
Mallinder went to ground after a huge hit after just three minutes of the European Challenge Cup clash at Franklin's Gardens.
He tried to battle on, staying on the field for a further two minutes before he was forced off.
And Boyd said: "He's done something to a knee probably.
"The feeling on the field at the time was that it didn't look to be too serious and he's got good strength and mobility in it.
"We're hopeful that it will be good news and not too serious."
Boyd admits some players who made it through the full 80 minutes were 'dead on their feet' at the end of an extremely physical clash with the Top 14 table-toppers.
He said: "Losing Harry early and Andrew (Kellaway) going to the wing, at the end of the game there were guys who were dead on their feet all over the paddock.
"We would have liked to have a medical intervention and got someone on to the field, but it wasn't to be."