Jonny Wilkinson was injured playing for Newcastle Falcons on Saturday a week before England's Six Nations clash with France, British media reported.
Wilkinson came off the pitch with what appeared to be hamstring trouble during Newcastle's 38-12 defeat by London Irish and will undergo tests over the next 24 hours.
Newcastle rugby director John Fletcher told the BBC: "He's just got cramp and that's why we took him off.
"All you can do with that sort of acute injury is ice it, there's nothing else you can do for 24 to 48 hours.
"I would imagine that there are some damaged fibres so we will just have to wait and see how bad it is, it'll just be a time thing."
The flyhalf's fitness for the France match will be a major worry for England coach Brian Ashton in light of Wilkinson's injury-plagued last three years.
England need a good performance against the unbeaten French in their fourth match of the tournament at Twickenham.
Wilkinson was in fine form in his first match for England since the 2003 World Cup final when he scored 27 points in the opening 42-20 win over Scotland a month ago.
That win raised hopes the team might recover from a slump in time to defend their title in France later this year.
But a disappointing display in the 20-7 victory over Italy followed by last weekend's 43-13 thrashing by Ireland exposed serious weaknesses.
Bath lock Steve Borthwick, who is back in the England squad and appeared in line for a place in the team, suffered a rib injury in his club's defeat against Worcester.
