Vaughan had scored 72 in Yorkshire's first innings

He was playing for Yorkshire against Hampshire when he was hit by a rising ball from Australian Stuart Clark.

He has an undisplaced fracture to the middle finger of his right hand.

"It looks like he might be out for three to four weeks, but it's too early to say with absolute certainty," said Yorkshire physio Scott McAllister.

Interview: Yorkshire's Darren Gough

Report: BBC Sport's Kevin Howells

"It's desperately bad luck for Michael after the succession of problems he's had to contend with, and we will be monitoring his progress over the next few days," he told the Yorkshire Post newspaper.

However, the England and Wales Cricket Board have not yet ruled the 32-year-old out of the match.

"Vaughan will undergo further assessment ahead of the first Test match against the West Indies at Lord's on May 17," read a brief ECB statement.

Vaughan has not played a Test match since December 2005, having sat out the whole of last summer and the winter Ashes series following knee surgery.

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He suffered a hamstring problem after making his comeback during the one-day series which followed the Tests in Australia, but recovered in time to play in all England's matches at the recent World Cup.

The match against Hampshire at the Rose Bowl was Vaughan's first since returning from the Caribbean and he looked in good form making 72 on the opening day.

He was 16 not out in the second innings when he was struck by Clark and forced to retire hurt. The fracture of his right middle finger was later confirmed by x-ray.

If Vaughan is ruled out of the first Test at Lord's, England will face a dilemma over who should replace him as skipper.

Andrew Flintoff led the team in the Ashes Tests, but was stripped of the vice-captaincy for disciplinary reasons during the World Cup and is unlikely to be elevated again.

It may therefore come down to a straight choice between Andrew Strauss, who stood in for Vaughan during last summer's series against Pakistan, or Paul Collingwood.

"To get mentioned with the captaincy is obviously a great feeling. But Michael's been doing a fantastic job. He may yet be fit for that first Test so we'll just going to have to wait and see," said Collingwood.

"I've done a few games for Durham a couple of seasons ago.

"I enjoy the challenges of captaincy but, as I've said, hopefully this will be in the future and hopefully Michael Vaughan will be fit."