The remainder of this season's Champions Cup and Challenge Cup have been postponed because of the coronavirus pandemic.
The quarter-finals of both competitions were scheduled for the first weekend of April but have already been suspended.
European rugby officials are still hoping to complete the campaigns this season.
Both finals had been scheduled for the weekend of May 22-23 in Marseille.
"It is planned to reschedule the quarter-finals, semi-finals and Marseille finals," a statement said.
It added: "All contingencies are underpinned by the requirement to protect the health and welfare of players, club staff, match officials, supporters and the wider rugby community.
"It is planned to reschedule the quarter-final and semi-final matches, as well as the Marseille finals, in line with fixtures in the professional league competitions, subject to advice from government and local authorities."
Ulster are scheduled to play Toulouse in the quarter-finals of the Champions Cup.
The remainder of the Guinness PRO14 season was suspended indefinitely last week.
