The European Challenge Cup quarter-final between Leicester Tigers and Castres has been cancelled 24 hours before kick-off due to three players and one staff member in the visiting party contracting coronavirus.
A medical committee convened on Friday ahead of Castres' planned departure to head to Welford Road for the clash on Sunday.
The decision was made that the quarter-final "could not go ahead safely in the circumstances".
European Professional Club Rugby has confirmed Castres must forfeit the match and Leicester will now qualify for the Challenge Cup semi-finals.
The full statement issued on Saturday afternoon said: "EPCR has decided to cancel the Challenge Cup quarter-final match between Leicester Tigers and Castres Olympique which was scheduled to be played tomorrow (Sunday, 20 September) at Welford Road.
"The decision followed a meeting of a medical committee comprising medical leads from the unions, league bodies and both clubs, and subsequent independent medical advice.
"The committee, chaired by Rod McKenzie (Scotland), met by video conference last night (Friday, 19 September) following confirmation by Castres that three members of their playing group, as well as one staff member, had tested positive for Covid-19 in advance of the club’s planned departure to England.
"It was decided on medical advice that the quarter-final could not go ahead safely in the circumstances and as a consequence, Castres have to forfeit the match and Leicester will qualify for the Challenge Cup semi-finals."
Leicester Tigers added in a statement: "Leicester Tigers have taken the position throughout the Covid pandemic that safety must come first as the club has a responsibility to its players and staff, to our city and county, and to our whole community.
"While the return of professional sport is welcomed as we approach the climax of our domestic and cross-border tournaments, there is also a responsibility to the game of rugby and to the protection of colleagues within Premiership Rugby and European competition with more rounds of fixtures still to be played.
"It is disappointing to reach this position after all of the hard work put into restarting fixtures in the professional game across Europe, but safety and wellbeing must come first.
"We wish a full and speedy recovery to anyone affected at Castres Olympique and send them our best wishes for the rest of the season."
