Saracens back-rower Billy Vunipola could miss the first month of the Aviva Premiership season in England as he continues to recover from shoulder surgery.
England international Vunipola pulled out of this summer's British and Irish Lions tour to undergo a shoulder operation, and has since been working back to full fitness.
Saracens rugby director Mark McCall expects the talismanic forward to be back in action ahead of schedule, but conceded that may not be before October.
"Billy's due back some time in October, but in true Billy style he'll make it back considerably before that," said McCall of England number eight Vunipola.
"He's in great condition at the moment and chomping at the bit.
"I'll be told by the medics when we can pick him but it won't be long."
Saracens will open their Premiership campaign against Northampton at Twickenham on September 2, with boss McCall reserving the final decision on whether to rush any of his six Lions tourists back into action.
Lock George Kruis could be in line to feature, with new recruit Will Skelton continuing to recover from a broken arm.
While the season opener may come too soon for Mako Vunipola, Jamie George, Owen Farrell, Maro Itoje and Liam Williams, McCall insisted he will consider each player's individual situation before reaching a decision.
"We've got a game coming up in 10 days and we need to take a long view with most of them," said McCall.
"To rush them back too early if we didn't have to would be a mistake in a couple of cases.
"But where the team needs that to happen then it may be that we need to bring one or two back for the first game.
"You need to look back over the past couple of seasons and who played how many minutes.
"A couple of players didn't play that much last year.
"Someone like George Kruis didn't play in the last two Lions Test matches, others missed a bit of rugby.
"With Mako (Vunipola) and Owen (Farrell) we have some tough choices to make.
"As a club we're not looking to get our pound of flesh. We're looking at the welfare of the player.
"I'm trying to make good choices based on good reasons as to when they come back."