Foley's side are unbeaten in their last five games in the GUINNESS PRO12 and sit top of the table but were undone early on at Thomond Park on Saturday as both Fritz Lee and Wesley Fofana crossed for tries in the first-half.
And while the men in red did manage to muster a response it was too little too late as the French side held on for a 16-9 victory, only Munster's third home loss in 53 European games.
The Irish province will now head to France for the return clash against their conquerors and Foley admits his side will have to up their game to keep any hopes of progressing from their pool.
"We're not going to throw in any towel. We'll give it our best shot and make sure we stay fighting," he said.
"We need to stay true to the badge we wear. It's not a great feeling at the moment. We need to rectify that.
"It's an unbelievably hard place to go. I've played there a couple of times. The crowd will be behind them.
"Similar to what you expect when you come here as an away side. Our crowd was in the game today, but unfortunately we couldn't aid them in getting a better performance out of ourselves."
Meanwhile reigning GUINNESS PRO12 champions Leinster are also going to have to produce a response after Harlequins won 24-18 at the Stoop on Sunday.
After tries in a five-minute spell approaching the hour by Nick Easter and Aseli Tikoirotuma left Leinster 21-12 down, the Irish province did fight back to claim a losing bonus point.
"I thought we came back into it very well against a very motivated side, they can get away from you pretty quick," said O'Connor.
"The (bonus) point is important. There's no question. At the end of the day, at the end of the group stages, that point could be the difference. We'll take that, lick our wounds and make sure we will be better next week."
It was better news for the third Irish region in the Champions Cup as Ulster reignited their hopes of making the knockout stages with a bonus-point 24-9 win over Scarlets.
Darren Cave, Ruan Pienaar, Tommy Bowe and Rory Best all crossed against their GUINNESS PRO12 rivals ahead of next weekend's return clash in Wales.
It was a tough time for Welsh sides as Ospreys, so impressive at the start of the domestic campaign, had to settle for a 19-19 draw at home to French powerhouses Racing Metro.
In the same group Treviso struggled to contain Northampton Saints, the English champions running in six tries in all in a 38-15 win in Italy.
Elsewhere in the Champions Cup Glasgow Warriors narrowly missed out on a losing bonus point in France as Toulouse held on for a 19-11 victory to stay top of their pool.
In the Challenge Cup Edinburgh set aside their stuttering domestic form to claim a 25-14 win over London Welsh on Sunday, while Zebre went down to a 35-10 defeat to Gloucester.
Cardiff Blues impressed on Saturday in claiming a 24-14 win over London Irish while Connacht turned on the style in beating Bayonne 42-19.
And finally Newport Gwent Dragons got their European campaign back on track with a 37-10 win over Bucharest Wolves.
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