Boss Jim Mallinder has vented his frustration over the fact Northampton have two days less preparation time than Castres ahead of their meeting.
Mallinder, whose side won 24-15 with a bonus-point against Glasgow, face a side that tackled Ulster in Round 1 a couple of days after them.
That has led to talk of the French being fresher when the two outfits run out at Stade Ernest Wallon, with Mallinder questioning the schedule.
"I think it's not quite right that they've got seven days to recover and we've just got five, having to travel to France as well, but that's the way it is," he told the Northampton Chronicle and Echo.
"You don't know what a Castres side will be like. We're playing in Toulouse which will be a different experience for us but it's one we'll really look forward to.
"It's a massive challenge playing in France but if we play at the top of our game we've got a good chance of winning it."
Saints are not alone in having less time to recover, however, as Glasgow Warriors also face the prospect of taking on a side that has had more rest, Ulster, in their Round 2 fixture.
"I'm sure Glasgow will take a lot of positives from that performance (on Sunday) and they deserve to," he said.
"We didn't underestimate them, we looked at the games and we saw they were playing well. They didn't win the previous four games by a fluke.
"They're a good side and hopefully they can win some of the other games and make it easier for us."