Back-to-back Premiership winners Saracens breached salary-cap rules in each of the last three seasons, but retained their titles.
An easing of lockdown measures means rugby players could return to training, but the RFU says further work is needed before that can happen.
The Highlanders confirmed the signing of former All Blacks wing Nehe Milner-Skudder.
Super Rugby Aotearoa, to be played by New Zealand's five teams, will begin on June 13.
Maro Itoje and Mako Vunipola have not committed to Saracens for next season, but John Mitchell is confident they will make the right call.