London - Dylan Hartley's chances of a place in England's Rugby World Cup squad were further hurt when he was ruled out of this weekend's English Premiership semi-finals meaning he has missed most of the European season.

Northampton visit Exeter on Saturday and had hoped to have the 33-year-old hooker back from a knee injury that has sidelined him since mid-December.

But Saints director of rugby Chris Boyd told Britain's Press Association on Wednesday that they would not be risking Hartley against the Chiefs.

"Dylan won't be ready to play," Boyd said.

"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."

Hartley, as captain and then co-captain, was a mainstay in the early years of Eddie Jones' reign as England coach following the Australian's appointment after the team's first-round exit on home soil at the 2015 World Cup.  

But he will now have to stake a claim for a place at this year's edition in Japan, which starts in September, after more than six months on the sidelines.

"His time will come when he's ready," Boyd added. 

"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."