Mardy Fish has withdrawn from the upcoming US Open amid concerns over his health.
The 31-year-old American, who is ranked 173rd in the world, has been blighted with heart problems during the past two years.
He tweeted: "Friends, unfortunately my health won't allow me to compete this year at the US Open. Thank you for all your support."
Fish reached a career-high ranking of seventh in the world in 2011 before the start of his health issues.
