Ryan Sidebottom has been pulled out of Yorkshire's team for their vital Cheltenham and Gloucester Trophy clash with Worcestershire at New Road tomorrow because of a tight hamstring.

The left-arm seamer was taken off during his first over in Phoenix's match with Glamorgan Dragons at Headingley on Sunday after bowling five wides and having his other delivery hit for six.

After further treatment on his hamstring yesterday, Yorkshire decided not to risk Sidebottom at Worcester and he has been replaced in the squad by 18-year-old paceman Tim Bresnan.

Geoff Cope, Yorkshire's director of cricket, said: "It appears as if Ryan's hamstring is stiff rather than torn and he needs a few days' rest in order to avoid making the injury more serious."

Yorkshire captain Anthony McGrath responded well to treatment yesterday on the side strain he picked up on his Test debut at Lord's, but whether he will be fit to lead his side tomorrow still depends on the outcome of a scan.

"We are arranging for the scan at England's request and if the result is not going to be known until Wednesday morning then McGrath may travel with Yorkshire so that we can delay a decision until the last minute," said Cope.

Although Yorkshire will have Michael Vaughan, Matthew Hoggard and Darren Gough in the side, plus new Indian signing Yuvraj Singh, they will still be happier if the batting can be strengthened by the presence of McGrath.

With the season crumbling around them, this is a game which they cannot afford to lose but the C&G champions will be severely tested by Worcestershire, who are in top form.

In their last Championship match they overpowered Second Division leaders Gloucestershire by 111 runs and on Sunday they thrashed Kent by 139 runs, Graeme Hick plundering 108. With their attack sharpened by the presence of the South African pair of Nantie Hayward and Andrew Hall they are a dangerous side against any opposition.

Yorkshire have only met Worcestershire once previously in the summer's premier one-day competition and that was at Headingley in 1982 under its NatWest sponsorship. All seemed lost for Yorkshire when they stood on 38 for four in reply to Worcestershire's 286 for five in the 60-over contest, but on the following morning of the rain-affected match they were seen home with three balls to spare by brilliant batting from David Bairstow, Chris Old and Neil Hartley.

Yorkshire (v Worcestershire) from: Wood, Vaughan, McGrath, Craven, Lumb, Yuvraj, Blakey, Gray, Gough, Silverwood, Sidebottom, Hoggard, Fellows.