Courtney Lawes is set to have a scan after missing Saints’ win against Gloucester with a knee injury.
Lawes, who did play against Castres last weekend, was initially named in the team, but had to pull out at late notice, with Michael Paterson stepping in to start and Api Ratuniyarawa on the bench.
After Friday night’s game, Saints boss Jim Mallinder was asked why the England lock had missed the match, just as he did the home game against Montpellier two weeks ago.
And Mallinder said: “Courtney has a bad knee, he did it a couple of weeks ago and missed the Montpellier game with it.
“We thought it had improved and he played last week with no problem, but midweek in training it reacted so we will have to have a scan on it to see the extent of the injury.
“I am not sure if he will be ready for the autumn internationals, fingers crossed there is not too much damage and he will be ready in a couple of weeks’ time.”
Calum Clark and Harry Mallinder were both forced off in the win against Gloucester.
And Mallinder said: “He (Clark) got a blow to the head so he’s sat there in the changing room and he’s a little bit groggy still so it’s very frustrating for him and the team.
“Harry took a bit of a blow to his ankle so fingers crossed that’s not too serious.”