England captain Michael Vaughan could miss the first Test against New Zealand starting at Lord's on Thursday after injuring his right knee in practice on Monday.
The England and Wales Cricket Board (ECB) said Vaughan is a "serious doubt" and Middlesex batsman Andrew Strauss has been called up as cover.
Vaughan hurt his knee facing a delivery from a member of the MCC groundstaff in the nets at Lord's and was carried off the field on a stretcher.
He later underwent a scan at a nearby hospital.
"I went to play a sweep shot against one of the net bowlers and ended up on the floor," Vaughan said on the ECB website.
"As I went to get up my body twisted and I felt me knee lock. It's very frustrating after doing so well in the West Indies and it looks like I'm a doubt for Thursday."
ECB chief medical officer Peter Gregory said: "The scan showed no significant damage to the knee ligaments.
"However, Michael has a previous history of cartilage problems with the right knee and may have aggravated an old injury.
"At this stage he is a serious doubt and will continue to receive treatment over the next 48 hours."
If Vaughan does not recover, fellow opener Marcus Trescothick would probably captain the England side.
