Kruis knee injury adds to England Six Nations worries

George Kruis a key member of the England side that completed the Six Nations Grand Slam last year could be in doubt for Saturday's opening game with France after suffering a knee injury on Tuesday.

The 26-year-old lock -- who has just recovered from a fractured cheekbone -- is to undergo further tests on Wednesday to ascertain the extent of the injury.

"George Kruis will go for further medical assessment tomorrow morning (Wednesday 1 Feb) to determine the extent of a knee injury picked up in training today," read the statement form the Rugby Football Union (RFU).

England and coach Eddie Jones -- who is defending a 13 match winning streak since taking over after the 2015 World Cup -- have had their Six Nations preparations disrupted by a series of injuries to players.

Wing Anthony Watson is out for at least two matches -- the French match and Wales in Cardiff on February 11 -- because of a hamstring injury.

Former captain Chris Robshaw is set to miss the entire tournament after undergoing shoulder surgery, while fellow loose forward Billy Vunipola will miss at least the opening rounds with a knee injury.

Meanwhile experienced back row James Haskell is struggling to overcome the lingering effects of a foot injury.

Vunipola's brother prop Mako is also out but fortunately for Jones his understudy Joe Marler has made a remarkable recovery from a fracture to his lower left leg.

Injury-prone centre Manu Tuilagi will play no part owing to a season-ending groin injury.

England are on a 14-Test winning streak, 13 of those victories coming since Australian coach Eddie Jones took over after their 2015 World Cup debacle on home soil.

They are set to be captained once again by Dylan Hartley.

The France match will be the Northampton hooker's first competitive fixture since he served a six-week ban for striking Leinster's Sean O'Brien.