Gaitan scored Biarrtiz's try in their quarter-final win over Munster

The Argentine international has been ruled out of the rest of the season and could be out for up to eight months.

He will be replaced by either compatriot Federico Martin-Aramburu or France A cap Guillaume Bousses.

Biarritz captain Thomas Lievremont and wings Jimmy Marlu and Jean-Baptiste Gobelot will have late fitness tests.

Stade Francais also have major injury problems ahead of Saturday's clash at the Parc des Princes.

Fly-half David Skrela damaged rib ligaments in Stade's 24-15 win over Castres last weekend and will miss the semi-final.

Two possible replacements, Gonzalo Quesada (thigh) and Brian Liebenberg (ankle) are also unfit, while fellow backs Juan Hernandez and Ignacio Corleto are also on the unavailable list.

Scrum-half Jerome Fillol, grandson of former France captain Guy Basquet, is set to start at fly-half.

"I am not too worried," said Fillol, whose last outing in the number 10 jersey was 12 years ago in a youth match.

"Of course normally I have more to do with the forwards than the backs in terms of gathering possession but now that changes as I will have to open up the back division."

Experienced France prop Sylvain Marconnet sat out training on Tuesday with a back complaint but is expected to be fit.