James Anderson is set to have a scan on his calf injury, with England hoping for good news ahead of next month's Ashes series.
Anderson, the country's leading wicket-taker and a major part of their plans to beat Australia, pulled up while attempting to bowl on day three of Lancashire's Specsavers County Championship match against Durham.
The 36-year-old only returned to bat briefly with a runner and did not bowl for the remainder of the drawn game.
The problem was initially described as "tightness" by his county, while Anderson posted on Instagram that it was "a niggle but hopefully not too serious".
The England and Wales Cricket Board elaborated on Thursday, saying: "Jimmy will have a scan tomorrow, late afternoon. We will assess further over the weekend."
Anderson has been in prime form for the Red Rose this season, taking 30 wickets at an average of under 10 in his six matches so far.
The first Test against Australia begins at Edgbaston on August 1, with five matches in six weeks placing a considerable physical burden on the players.
There is also a standalone Lord's Test against Ireland starting on July 24, with Anderson's chances of appearing in that game receding due to the current scare, despite the prognosis.
