Andy Farrell has been ruled out of Saracens' Premiership opener against champions Wasps at Twickenham on Saturday.
The former Great Britain rugby league captain, who moved to Saracens in a deal jointly-funded by his club and the Rugby Football Union earlier this year, is still recovering from a toe injury.
Saracens rugby director Steve Diamond had hoped to include Farrell in one of the club's pre-season friendlies against Bedford or Harlequins, but his eagerly-awaited union debut remains on hold.
"Obviously, we had hoped that Andy would have fully recovered from the problem, but he is not quite ready yet," said Diamond.
"We hope he will be able to return to full training soon, and he may be in contention for our game against Leeds at Vicarage Road on September 11."
Farrell's fellow union convert, former Bradford Bulls wing Tevita Vaikona, is also currently injured, while back-row forward Taine Randell misses the Wasps clash because his wife is due to give birth this weekend.
Robin McBryde was assistant coach with Wales during the Championship
27 March 2017, 11:19am
Wales secured wins against Italy and Ireland in the 2017 RBS 6 Nations but were beaten in Paris and Edinburgh as well as suffering defeat to England in Cardiff. Here we take a look at what lies ahead for Wales in the next 12 months.