Batsman Gibbs will miss Twenty20

Herschelle Gibbs played for Glamorgan in last summer's Twenty20 Cup

Glamorgan will play their last four Twenty20 matches this summer without an overseas player.

South African star Herschelle Gibbs' arrival has been delayed by commitments to South Africa's cricket board.

And with no chance of making the quarter finals, Glamorgan have opted not to retain Aussie opener Mark Cosgrove for first-team duties.

Instead batsman Mike O'Shea, 21, returns after serving a three-week ban imposed for a drink-driving offence.

Glamorgan cricket manager Matthew Maynard said: "We're desperate to win the matches but we may as well give our youngsters the opportunity.

"Mark's contract ended and we had Herschelle to come in but he's had to go back to South Africa for a Cricket South Africa function."

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Cosgrove will remain in Britain to play Lancashire League cricket and will be available for Glamorgan second team matches during the week - as well as being on standby if there are any problems with Gibbs' availability.

The move could be a pointer towards next season when counties will be able to field up to four overseas players in the new P20 Twenty20 event in the middle of the campaign, with Cosgrove's hard hitting style and ability to bowl medium pace ideally suited for the competition.

Glamorgan claimed only one win from their first six matches in Twenty20 before the break in the domestic competition to accommodate the international event in the same format, with just one home fixture left against Northants on Friday in the four remaining fixtures.

The results have been a disappointment after Glamorgan's 50 per cent record at the group stage last season was enough

"We wish O'Shea and the other youngsters all the best for the tournament," said Maynard.

"It gives us the opportunity to juggle a couple of things and use it as an experimentation."