Maro Itoje is being assessed by medics after the England lock gave Eddie Jones a scare ahead of Saturday's Guinness Six Nations clash with Italy by hobbling out of training.
Itoje was on course to make his comeback from the ligament damage sustained to his right knee against Ireland on February 2 but the setback in training on Tuesday morning has placed that prospect in doubt.
The imposing British and Irish Lion was performing a forwards drill when he appeared to hurt the same joint as he made a side-step and after falling to the floor in obvious pain he limped off.
The injury was sustained in front of head coach Jones, who was feeding the forwards the ball as they ran towards the posts.
Attack coach Scott Wisemantel insists the injury is not significant and refused to rule the 24-year-old Saracen out of Italy's visit to Twickenham in the penultimate round of the Championship.
"Maro has had a minor tweak and the medical staff are taking a look at it. He's being managed day by day anyway. I don't think it's anything serious," Wisemantel said.
"We've just got to wait and see what the medics say. We'll see how he pulls up tomorrow (Wednesday)."
Itoje was replaced in the first half of England's rout of Ireland in their Six Nations opener and the prognosis for his return from a grade two medial ligament tear was two to four weeks, potentially enabling him to feature against Italy and Scotland.
Courtney Lawes was lost to a calf strain sustained against Wales and England were banking on Itoje being available for Italy, hence the inclusion of only three locks in their 31-man training squad.
Conor O'Shea's Azzurri have lost their last 20 Six Nations matches in a dismal sequence dating back to 2015.
Wisemantel, whose appointment to Jones' management team has coincided with England's flourishing attacking game, views the fixture as the platform for minor experimentation.
"It's an opportunity to change a few things, so we'll look to mix it up a little bit," the Australian said.
"But look at the teams who have played Italy – they haven't changed a lot. Scotland, Wales and Ireland have stuck to their structures and we won't go too far away from ours.
"It will be interesting to see what Italy bring, so we've prepared for all sorts of scenarios.
"It's a really exciting prospect because it freshens up the programme and freshens up the players and makes them explore possibilities. It's good."
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