Brad Shields in World Cup fitness race after foot injury in training

Shields last week returned home from the warm-weather training camp in Treviso after sustaining ligament damage and could miss all four warm-up games, starting with Wales at Twickenham a week on Sunday.

"Brad's got a tear in the lower foot. It's always a little bit niggly, but it's four to six weeks for him," assistant coach John Mitchell said.

"Obviously we've got a deadline and that's important, but (head coach) Eddie Jones will decide on who's right and who's not right. There's plenty of time to go."

Jones must make a call on Shields before August 12 when he names his 31-man squad for Japan 2019.

If fit, the New Zealand-born Wasps flanker would be a strong contender to travel, but with Mako Vunipola, George Kruis and Jack Nowell also in various stages of rehab, the squad would be in danger of carrying an escalating number of injured players.

Mitchell was able to deliver a positive update on Kruis, however, with the Saracens lock making a return to training this week having undergone ankle surgery.

Vunipola, a certainty for inclusion in the 31, is making encouraging progress in his recovery from a hamstring complaint, but England have yet to set a date for his comeback.

"George been fantastic and the medical team have done a great job on his progressive return and he's back in, full of enthusiasm and looking great," Mitchell said.

"Mako's progressing nicely, so we should see him back at some point in August."

England are awaiting an update on Nowell, who returned home on Monday for a routine surgical review having gone under the knife to repair ankle damage.

The 12-day 'heat camp' in north-east Italy that ends on Friday is designed to mimic the conditions in Japan, where September and early October can produce high humidity.

"The heat here isn't so bad, it's about 34-36 degrees, but the other thing is the variance in the humidity," Mitchell said.

"For those of you that have experienced any sort of form of exercise in humidity, you'll know it takes a while to adapt.

"We've had humidity ranging between 75 and 90 per cent here. It makes you sweat and it sits on you as well, so the intake of fluid and electrolytes is critical every day.

"It's certainly asking good questions and greater demands on work-rate off the ball and the little things that are unseen when you're challenged by heat and fatigue."

Assisting England's preparations have been Italy, who on Monday provided training opposition ahead of a match between the sides in Newcastle on September 6.

"It's always nice at some point during your preparation to train against an organised opposition that you're not familiar with on a day-by-day basis," Mitchell said.

"It was really constructive and very unemotional, which can often not be the case when you have forwards up against forwards. Both countries got a lot out of it."