Grayson, who has scored 133 points in just eight games for England, faces an anxious battle to be fit and Northampton's rugby director, Ian McGeechan, said: "The muscle has been torn and there is internal bleeding. But if it is just that he has got a fighting chance of being fit for Cardiff.
"He has already had two treatment sessions with our physio this morning and he and Paul need to get rid of the bleeding before they can properly assess his condition. Obviously he will not play for us this weekend."
Grayson said: "I felt something pop after my first goal-kick and within a few minutes had no option but to go off."
If he does not recover, Jack Rowell, the England coach, will be limited by the few first-choice English stand-offs playing in the top flight. The obvious choice would be a return for Mike Catt, who has had two brief spells in the position before being dropped in favour of Grayson in both the last two seasons. The riskier option would be to give first caps to either of the England A stand-offs, Alex King or Mark Mapletoft.
But there was better news of another England player who limped off on Tuesday night after the Saracens flanker Richard Hill confirmed that he should have recovered from his ankle problem by the weekend.
Wales will definitely have to decide on a new outside-half for the England game as Arwel Thomas had to pull out yesterday because of a partially torn ligament in his right knee. The Swansea No 10 conceded that his chances of forcing his way into the Lions squad for the tour to South Africa were now over.
Thomas's position looks like being filled by either Jonathan Davies or Neil Jenkins. Jenkins has played at full-back throughout the Championship, despite remaining at outside-half for Pontypridd, while Cardiff's Davies has extended his cap collection to 31 this season with appearances against Australia, the United States, Scotland and France.
BBC Television are breaking with tradition and showing both of the season's final Five Nations matches live. The BBC plan to show France's match against Scotland in Paris and Wales' game against England in Cardiff simultaneously. France will have the first half of their Grand Slam decider shown on BBC1, with the second half switching to BBC2.Reuse content