Juan Martin del Potro has withdrawn from next week's Aegon Championships at Queen's Club because of injury, putting his participation at Wimbledon in doubt.

Former US Open champion Del Potro is still struggling with a groin problem that hampered him at this year's Roland Garros -- where he lost to Andy Murray in the third round.

British No. 3 Dan Evans has also withdrawn from the Aegon Championships -- and like Del Potro -- faces a race to be fit for Wimbledon after suffering a calf injury at a tournament in Surbiton last week.

Dan Evans suffered a calf injury at a tournament in Surbiton last week. Al Bello/Getty Images

Evans had to retire during his quarterfinal against Dustin Brown and was seen on crutches after pulling out of this week's Aegon Open in Nottingham.

James Ward has been given a wild card into the tournament as he continues his comeback from a knee injury.

The 30-year-old, a key member of Great Britain's Davis Cup winning team in 2015, was a semifinalist at Queen's in 2011 but is currently ranked outside the top 1000.