Eddie Jones has cited England's lack of leaders as one of the biggest stumbling blocks to winning the 2019 World Cup.

England boss Jones rates captain Dylan Hartley "seven out of 10" in fitness terms for the RBS 6 Nations, following the Northampton hooker's latest suspension.

Head coach Jones insists Hartley remains firmly "in the reckoning" to start England's Six Nations opener against France at Twickenham on Saturday, February 4.

When quizzed on England's captaincy options that fall behind regular skipper Hartley, Jones answered: "There's not many".

Asked if that lack of leaders causes him problems, Jones replied: "Oh 100 per cent, that's one of our great keys going forward.

"Apart from working on the fundamental skills and increasing the depth of the squad, one thing we need to do is increase the leadership density of the team. That's a big project going forward.

"Dylan Hartley is moving in the right direction.

"In the autumn we would have given him five out of 10, in terms of ready to play, and now he's about a seven out of 10.

"Given that he has a good couple of days of training in our camp in Portugal I'd anticipate him being in the reckoning for the first Test team.

"I'll have a look at him on Monday and Tuesday."

Hartley was sent-off in Northampton's defeat by Leinster and banned for six weeks (Getty)

England captain Hartley will have served his six-week suspension for striking Leinster's Sean O'Brien just in time to return for the Six Nations campaign.

But despite rigorous fitness testing this week, the Northampton front-rower must still fully convince boss Jones he is fully ready for the Test-match arena.

The 30-year-old took his career suspension tally to 60 weeks with his latest ban, but Jones remains unfazed about that element of Hartley's robust approach.

England head to Portugal on Sunday for a three-day warm weather training camp, to crank up preparations for the Six Nations opener against France.

Hartley's readiness for Test rugby will come under further scrutiny in that camp, but the 78-cap front-rower appears to be winning his battle to start the Six Nations right from the off.

George Kruis is one of Jones's injury concerns ahead of the Six Nations (Getty) (Getty Images)

Jones admitted England must "monitor closely" George Kruis, James Haskell and Joe Marler as all three return from injury, with Marler rated "51-49" in his battle to recover from a broken leg.

Former Japan boss Jones named Ellis Genge in his 34-man Six Nations squad, recalling the Leicester prop after a spell in the wilderness.

Uncapped Mike Williams, Nathan Catt and Alex Lozowski have all made the cut for England's tournament ranks.

While Jones fully admits England's top current aim is to retain their Six Nations title, the former Australia boss also conceded he is determined to build the leadership qualities in his squad.

"It's about developing players' leadership skills," said Jones.

"What is being a leader? Being a leader means every day you rock up to training, rock up to a meeting, and you get on with the job.

England are looking to maintain their winning streak under Jones (Getty) (Getty Images)

"You do it to absolutely 100 per cent.

"And if the guy next to you is not doing it properly, you tell him he's not doing it properly. And you tell him how to do it.

"When we've got 10 players like that, then we'll be in a position to win the World Cup. We're not there at the moment, but we'll get there.

"And we've got to look at each player that potentially has those set of skills, and work out how we can improve that player. Whether he needs help in his presentation skills, whether he needs help in his assertiveness skills.

"It's all about professionally and personally developing the players."