Graeme Dowell has been forced to withdraw from the Valero Texas Open in San Antonio midway through his opening round due to a leg injury. 

The Portrush man had been playing with strapping on the strained ankle and was five over par through nine holes when he was forced to retire from the event.

The injury is not believed to be serious enough to threaten the 35-year-old's participation in the Masters, which begins a fortnight today at Augusta.

McDowell, who won the US Open in 2010, was five over at the when he withdrew, having started on the back nine.

McDowell is also scheduled to take part in next week's Houston Open.