The Champions Cup quarter-final between Toulouse and Ulster this month has been moved to the Stade Ernest Wallon because of Covid-19 restrictions.
The Top 14 side had initially planned to host the 20 September game at the 33,000-capacity Le Stadium.
The Stade Ernest Wallon holds up to 19,000 people but attendance will be limited to 5,000 for the Ulster game due to restrictions on gatherings.
The winners will play Exeter or Northampton in the semi-finals.
Local authorities have imposed the 5,000-spectator limit and an appeal from Toulouse for an exemption was rejected.
"Knock-out games at home are always great moments of sport, which is so big in our city," said Toulouse president Didier Lacroix.
"Playing this quarter-final at a reduced level frustrates us enormously - by relocating the quarter-final to Ernest Wallon and with the attendance limited to 5,000 people, we are dividing our possible revenues by eight times."
Toulouse said it plans to ensure season ticket holders and commercial partners are prioritised for available tickets.
Ulster completed a Champions Cup double over four-time winners Toulouse when sides last met in the competition in 2015.