Toulouse's forward coach Jean Bouilhou said his side were distracted after being beaten 32-28 at home by struggling Bayonne in the French Top 14 on Saturday as Cheslin Kolbe was rested a week before the European Champions Cup final.
South Africa's Rugby World Cup winner Kolbe and former New Zealand back-rower Jerome Kaino were among those given the weekend off ahead of facing La Rochelle at Twickenham next Saturday.
Toulouse remain top, however, despite a first home loss to the Basques since 2006.
The result saw Bayonne go three points clear of Pau in the relegation play-off spot, with two games of the regular season to go.
"We won't keep much from the match. Maybe the fact we had a double objective, it's not easy to prepare with that in mind," former Toulouse back-rower Bouilhou said.
"We blew what we thought would be a breeze, it's the last one."
Bayonne fly-half Maxime Lafage slotted 19 points in the win after former Samoa lock Joe Tekori and France full-back Thomas Ramos crossed for tries to help put the league leaders 14-0 up after just a quarter of an hour.
Toulouse winger Dimitri Delibes crossed with two minutes to go to claim a bonus point which handed his team a guaranteed place in the end-of-season play-offs between the top six teams. They remain in pole position for a direct spot in the semi-finals.
- Rhule the roost -
It was a different story for La Rochelle as South Africa winger Raymond Rhule claimed a try double in a 59-0 hammering of already-relegated Agen.
Head coach Jono Gibbes welcomed back numerous starters after resting the likes of former All Blacks Victor Vito and Tawera Kerr-Barlow as well as Australia lock Will Skelton for two losses in three days earlier this week.
La Rochelle returned to second in the table, leapfrogging Racing 92 after the Parisians' win at Pau on Friday.
Elsewhere, Racing's cross-capital rivals Stade Francais kept their hopes of a play-off place alive with a 32-10 victory over Montpellier, who had made 14 changes ahead of Friday's European Challenge Cup final with Leicester.
Montpellier's Springbok half-backs Handre Pollard and Cobus Reinach, who lifted the Webb Ellis trophy with Kolbe two years ago, were among those to miss the defeat.
"Handre's had a little calf issue. He's working a lot," Montpellier coach Philippe Saint-Andre said.
"I hope to have him back on Monday to prepare for the final."
Earlier, France fly-half Matthieu Jalibert kicked 15 points as Bordeaux-Begles overcame Castres 20-16 as they also eye a place in the top six places.
The late game saw another World Cup winner, Eben Etzebeth, making his first Toulon start in seven weeks, away at Clermont.
The Bok lock came on as a substitute in Tuesday's loss at Montpellier after recovering from a finger injury sustained in late March, but there was to be no joy Saturday as Clermont ran out 25-16 winners to consolidate their fourth place in the table, just a point off Racing.
Former France scrum-half Morgan Parra was faultless from the tee, booting six penalties and converting Fijian Apisai Naqalevu's late try for a personal haul of 20 points.
Toulon now lie seventh, with just eight points separating third-placed Racing and Lyon in ninth in what promises to be a desperate fight for a top-six place.