Pickering has a season's best of 10.38secs over 100m

Craig Pickering's Olympic preparations suffered a blow after he was forced to pull out of this weekend's European Cup because of a minor hamstring strain.

The sprinter, 21, withdrew from the 4x100m relay in France as a precaution after an injury-disrupted season.

Pickering is a vital part of Britain's relay squad who will defend their Olympic crown in August.

UK Athletics performance director Dave Collins: "Obviously Craig's focus is on getting to Beijing in top form."

Pickering, who will now focus on the Olympic trials on 12-13 July, missed the World Indoor Championships in March because of the same injury and has run only once this summer.

He has been replaced in the European Cup squad by Simeon Williamson, who finished seventh in the 60m final at the World Indoors in March.

The meeting in Annecy this weekend offers the team the chance to practice their baton exchanges under the pressure of competition.

Tyrone Edgar, the fastest Briton over 100m this season, will contest the individual race in France.

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"Being able to draft an athlete of Simeon's calibre into the relay squad shows the strength and depth of British sprinting."

Britain's hopes of defending their 4x100m Olympic title were diminished when a pre-season Achilles injury ruled out Mark Lewis-Francis, who ran the anchor leg in Athens.

Dwain Chambers is also unavailable because of his lifetime ban for taking drugs.

Worries over Pickering's fitness add to Britain's track and field concerns ahead of the Beijing Games.

Heptathlete Jessica Ennis has been ruled out with an ankle injury while marathon world record holder Paula Radcliffe remains a major doubt with a stress fracture.

Lee McConnell and Tim Benjamin have also withdrawn from their respective 4x400m relay teams ahead of the European Cup while Richard Hill replaces Michael Rimmer in the 800m.