Two of England’s key players, the captain Dylan Hartley and the goalkicker Owen Farrell, are struggling to shake off back injuries as Eddie Jones prepares to name his 32-man squad for autumn’s Twickenham internationals.

Hartley is not expected to return for another two weeks while Saracens remain unable to confirm when Farrell will be able to play his first game of the season.

The Saracens director of rugby, Mark McCall, speaking at the European Champions’ Cup launch in London, conceded Farrell’s fitness is a slight concern as his team prepare to launch their defence of the trophy.

“It is a back injury but it is not one where the physios are able to tell you he will be back by this or that point,” said McCall, whose side face Scarlets, Toulon and Sale in the group stage. “It’s frustrating for him, it’s frustrating for us but he can’t play until he is ready.”

Facebook Twitter Pinterest Owen Farrell’s back problem began in pre-season and he has not played for Saracens this season. Photograph: Adam Davy/PA

Farrell has been struggling to kick without experiencing pain, which is a worry for club and country. “It has taken longer than thought but it is no one’s fault,” said McCall, who insists his fly-half will not require an operation.

“It happened at the very start of his pre-season but he won’t play until he can do everything. We don’t think there is a worst case scenario; we think it is a matter of weeks.”

Hartley, who captained England to the Six Nations title last season, is at least back running but is not yet guaranteed to be available for the opening round of European pool games next month. He has been suffering from back spasms that have restricted his ability to lift heavy weights or scrummage.

“We are hoping he’ll return in the next couple of weeks but I don’t want to set a date,” said the Northampton director of rugby, Jim Mallinder. “What we don’t want is to play him for 40 minutes and him then to be out for another two weeks. We want to get it sorted properly and hopefully then will not affect him for the rest of the season.”

Jones has received some good news, with Jack Nowell poised to make his first appearance of the season off the bench for Exeter in Friday’s game at Northampton.

The World Cup-winning flanker Richard Hill has been appointed the England team manager.