The meeting was initially scheduled to take place on Saturday, before being postponed due to two positive Covid-19 cases in the Castres ranks.
The stakes are different for the two clubs.
Aviron Bayonnais, twelfth in the standings, has the opportunity to distance itself from the red zone.
The Basque club is three points ahead of Pau, in a barrage position, which lost Saturday in Paris against Stade Français (46-32).
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For his part, Castres wants to continue to maintain the hope of finishing in the top six to play the title.
A success would allow him to move from eighth to sixth place.
"We will have to go there with a lot of ambition, put a lot of fight and compete because they have the knife between their teeth with the pressure of Pau which returns", commented the third line international Anthony Jelonch at a press conference on Tuesday.
Castres remains on three victories, the last on April 17 against the leader, Stade Toulousain (26-24), who had played with a reshaped team.
Kockott's private CO suspended
Aviron Bayonnais meanwhile lost an important game for the maintenance against Pau (43-33) during their last outing.
But he was not unworthy in Castres (defeat 31-21) in the first leg in early February.
The Basque team will benefit from the return of second row Guillaume Ducat and winger Joe Ravouvou.
Castres will have to do it without his scrum half Rory Kockott, suspended.
Three other late matches are scheduled for Saturday: the Racing 92-Stade Français Paris derby, Toulon-Agen and another derby, Clermont-Brive.
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