Toulouse's goal-kicking scrum half Jean-Baptiste Elissalde could miss Saturday's Le Stadium de Toulouse showdown with Northampton Saints.
Elissalde, who can also play fly half, picked up a thigh injury in his team's 37-19 win over Bourgoin on Saturday and will have to wait for further examinations to determine whether or not there is a tear.
Toulouse head coach Guy Noves said: "Luckily, we have Yann Delaigue and Frédéric Michalak who are experienced half-backs in case Jean-Baptiste doesn't make it. Our performance will have to be 30% better than Saturday's if we want to beat Northampton - in terms of commitment and fitness levels, we will have to improve.
"Fortunately, we now have a whole week to work together as a group to prepare for the match, a luxury we have not had since the start of the Six Nations."
And Delaigue echoed his head coach's warning that the 1996 champions need to step up a gear. "If we produce the same performance as against Bourgoin on Saturday, we won't be going through to the semi-finals," he said.
"We made too many mistakes and our discipline wasn't good. Defensively, we will have to improve and offensively, we need to be more realistic and score when we are in the opposition 22. Our performance against Bourgoin won't be enough to win the Heineken Cup quarter-final against Northampton. Hopefully, we will play better as a team after a week training together."
Ireland international back row forward Trevor Brennan added: "It was hugely important to get a win on Saturday because our loss and our performance in our previous game at Biarritz was disappointing.
"We sometimes get called the Real Madrid of rugby union but you can't be a good team if you blow hot and cold. And, for me, you can't play a team like Northampton on the back of a loss - it was vital to get a win on Saturday.
"Saturday is going to be a huge step up from last weekend. Bourgoin only really have one current international whereas Northampton have 13 or 14 past and present internationals. They have five or six Lions, four or five current England players, Australians, All Blacks - their squad list really is impressive.
"If we play to the best of our ability and are in the right frame of mind, never mind about Northampton, we can beat any team in Europe. It's about getting the best out of the guys on the day and everybody giving 100%.
"It hasn't been easy during the Six Nations - before the Biarritz game, for example, the French international players only took part in the captain's run before playing in the match - it is not easy to cope with that kind of situation.
"Against Northampton, we will have to tighten up our game a bit - Matt Dawson likes to steal ball from around the rucks and mauls, it's important to close a player like him down.
"We will also have to stop their rolling mauls and hold our own in the scrum. At the end of the day, the players here really want to win the Heineken Cup - as much as the French Championship - and that starts on Saturday."