Unified welterweight world titleholder Keith Thurman, who has been out of action since last March because of right elbow surgery, has another injury that will keep him sidelined a bit longer.

Thurman suffered a deep bruise to his left hand and has been forced to pull out of his next fight, scheduled for May 19, a source close to Thurman told ESPN on Friday.

Keith "One Time" Thurman's return to the ring following elbow surgery will be pushed back due to a hand injury sustained in training. Al Bello/Getty Images

Thurman has not boxed since winning a split decision against Danny Garcia to unify two 147-pound world titles on March 4, 2017, at Barclays Center in Brooklyn, New York, in one of the most anticipated fights of the year.

After that fight, Thurman had surgery on his injured right elbow and was due to return in a Showtime-televised title defense scheduled for May 19, also at Barclays Center.

Thurman's opponent had not yet been announced for the May 19 fight even though Thurman's return had been announced in late January when Showtime unveiled its schedule for most of the first half of the year at a glitzy media event in New York.

Thurman (28-0, 22 KOs), 29, of Clearwater, Florida, suffered the injury about two weeks ago and was advised by his doctor to rest his hand for six weeks, the source said. Thurman is aiming for a summer return.

Thurman has made four title defenses since being elevated from an interim world titleholder to a full titlist in 2015.