The Professional Game Board said more work needs to be done before Premiership rugby teams in England can start training.
England international Harry Williams says he feels ready to move to another level after extending his stay with Exeter Chiefs.
A five-week break has been implemented in the Premiership, with the Champions Cup and Challenge Cup quarter-finals pushed back.
Exeter Chiefs have returned to the Premiership summit, while Wasps and Saracens also celebrated victories.
Exeter plundered eight tries in a crushing victory over Northampton as they took another step closer to finishing top of the Premiership.
Stuart Hogg was among the scorers on his Exeter Chiefs return as Gloucester were beaten at home.
Exeter Chiefs rallied in the second half against Sale Sharks, but the Premiership leaders still slipped to a first defeat since November.
Exeter Chiefs have announced Jack Nowell was overlooked by England for the Six Nations because he requires an ankle operation.
Northampton Saints and Glasgow Warriors did all they could to stay in the European Champions Cup, while Ulster are definitely through.
Rhys Carre's early red card made life difficult for Saracens, but they still defeated Ospreys in the European Champions Cup.