Courtney Lawes will need further medical tests to see the extent of the damage to his injured ankle after he went off in the first half of Northampton's 20-15 win at Saracens.
The England lock had to be helped from the field after getting his leg stuck in a ruck, and appears a major doubt to feature against Wales at Twickenham next week.
His injury overshadowed a fine win for Northampton, who scored a try in each half through Stephen Myler and Lee Dickson, but director of rugby Jim Mallinder played down its significance with the sides set to meet in Europe after the Six Nations.
He said: "Courtney is sore. He's twisted his ankle but we don't know the extent of the damage just yet.
"It's too early for me to say how he will be but he's a tough lad. I don't think he will want down time! He always wants to play and be given more minutes
"Any win down at Saracens is good. Even with their international players away it's a good win but I think it could be a different game come the European Champions Cup.
"I think our performance, particularly in the first half, was very good. And we came out in the second half and Dickson scored. We're slightly disappointed we couldn't finish off the (Ben) Foden opportunity but we are generally happy."
There was disappointment for Saracens, though, who were beaten for only the third time this season and paid the price for their international absentees.
Director of rugby Mark McCall admitted he was pleased to at least pick up a losing bonus point.
He said: "We got away with a bonus point, and we move on to the next game. We've asked a lot from this group in the last few weeks, the physicality and the intent was there, which is pleasing, but we were undone by the small things.
"In terms of the big stuff that you require week in week out, we were good. We just got the small stuff wrong, the details - knocking on three balls in good positions.
"This is a tremendously challenging period for us and it's been tough. Despite the fact we lost, I think we are going to be ok. We are all in the race to get into a top four spot and hopefully we have enough, especially with the cavalry coming back, to stay there."