Saracens' director of rugby Mark McCall insists Owen Farrell is progressing with his back injury but the club cannot set a return date.
The England fly-half has yet to play this season after picking up the knock during pre-season but the club have taken their time with his rehabilitation.
Farrell is currently struggling with his place kicking and the news will be a worry for England ahead of the autumn campaign.
The 25-year-old will miss Sunday's Aviva Premiership clash with Wasps but McCall insists he is improving each week.
He told reporters: "Owen trained on Thursday and trained as part of the opposition. That's a good, encouraging sign.
"The scan he had last week came back positively, so that's good. It's really a case of when can Owen do all the things he needs to play. Once he can, he'll play.
"He hasn't placed kicked, but he's kicking out of hands. I'm not sure if he'll be fit for the Toulon match, but his ability to go straight back in would be a consideration.
"I'm nervous about saying too much about it because he's just done a 45-minute training session and looked pretty good, but it's how he feels over the next 24 hours that's the important thing."