Dylan Hartley must stake his claim for a place in England's World Cup squad without playing since mid-December after he was ruled out of Northampton's clash with Exeter on Saturday.
Saints hoped the 33-year-old hooker would recover from his knee injury in time for the Gallagher Premiership play-off at Sandy Park but director of rugby Chris Boyd revealed that he has failed to recover in time.
As one of Eddie Jones' co-captains until injury struck, Hartley is certain to be picked in the wider World Cup training squad but he must prove he is worth a place at Japan 2019 despite more than six months out.
"Dylan won't be ready to play," Boyd told the Press Association.
"If there was no rugby to come in the next six months we might roll him out and see if he can get through it.
"But in such a crucial game and not having played since Christmas he's got some other stuff to get his head around so we've decided he's just not quite ready.
"If we had to roll him out for 20 minutes he could do that and get away with it, although how he'd be on Monday I'm not sure.
"I know that if he'd had to get through 75 minutes last week against Exeter last week when Reece Marshall went down with injury, he might have been in a wheelchair this morning.
"His time will come when he's ready. Hindsight is a wonderful thing, maybe we should have, or he should have, collectively, gone for the surgical option.
"We tried for rehab and it was unsuccessful so it hasn't been plain sailing for him. There have been a few false starts but you can't predict those things."
