Promoter Frank Warren informed Top Rank on Monday that lightweight world titleholder Terry Flanagan has suffered a leg injury, forcing his mandatory title defense against Felix Verdejo to be postponed, Top Rank vice president Carl Moretti told ESPN.

Although the bout had not yet been formally announced, Flanagan-Verdejo was scheduled to take place on Sept. 16 at the Copper Box Arena in London on the same card on which middleweight world titleholder Billy Joe Saunders (24-0, 12 KOs) will make his second defense against Willie Monroe Jr. (21-2, 6 KOs). Warren hosted a news conference on Monday in London to announce that fight, but did not address Flanagan-Verdejo.

An injury to lightweight titlist Terry Flanagan has forced the postponement of title defense against Felix Verdejo which was scheduled for Sept. 16. Dave Thompson/Getty Images

Top Rank and Warren made a deal for the fight several weeks ago and then, on July 6, Top Rank chairman Bob Arum finally was able to come to terms with Verdejo manager/trainer Ricky Marquez on their end of the bout. Now it is delayed.

"They're claiming that Flanagan has a leg injury. Frank sent an email to Bob (on Monday) morning," Moretti said. "He said that Flanagan sustained a leg injury and that they will get back to us shortly on rescheduling the fight.

"I just spoke with Ricky. They're disappointed, but Verdejo will continue training hard and we'll see what happens with the rescheduling of it, and plan accordingly."

Moretti said he was not aware of the specifics of the injury but that the WBO, which recognizes England's Flanagan (33-0, 13 KOs) as its 135-pound world titleholder, has requested that he provide the sanctioning body with medical certification of the injury.

Flanagan, a 28-year-old southpaw, has made five successful defenses, including a one-sided unanimous decision against rugged Petr Petrov in his most recent fight on April 8.

In February, Verdejo (23-0, 15 KOs), a 24-year-old who represented Puerto Rico in the 2012 London Olympics and was the 2014 ESPN.com prospect of the year, ended an eight-month layoff by winning a 10-round unanimous decision against Oliver Flores in San Juan. It was Verdejo's first fight since he crashed his dirt bike and spent five days in the hospital with an assortment of cuts, bruises and scrapes -- injuries that sidelined him for the remainder of 2016 and cost him a fall shot at Flanagan.