The UFC on FOX summer card lost its main event today with the news that headliner Brian Stann, who was set to face Hector Lombard, had been injured and forced to withdraw from the event.

The new main event on August 4 will be a five-round light heavyweight battle between two of the best Muay Thai strikers in the game, Brandon Vera and former champion Shogun Rua. Rua is riding the momentum of the fight of the century against Dan Henderson, while Vera is back in the win column and looking to make a statement after being sidelined earlier this year due to injury himself.

Rua is being plucked from the UFC 149 card in Calgary, where he was set to face Thiago Silva until Silva suffered an injury. Vera, meanwhile, was training for a bout with James Te Huna at the July FUEL TV event. A new opponent for Te Huna is expected to be named shortly.

“No one is more disappointed than I,” said Stann via Twitter. “Meant the world to headline a UFC.”

In other UFC on FOX 4 injury news, featherweight Pablo Garza has had to withdraw from a bout with Josh Grispi. Rani Yahya will step in as the the replacement, which may change Grispi’s game plan — Yahya is an ultra-dangerous grappling specialist with a near 90% finishing rate via submission.

Verbal agreements are in for both bouts.

Updated: Lombard will now make his UFC debut at UFC 149 in Calgary, Alberta, against Tim “The Barbarian” Boetsch. Lombard replaces injured British striker Michael Bisping.

Swick and Grispi Gear Up for Summer Returns updated May 22
Verbal agreements are in for two of Zuffa’s finest to make their long-awaited returns to action at UFC on FOX, taking place August 4.

Fan favorite Mike “Quick” Swick, who’s battled a barrage of illnesses and injuries, will make his UFC return after more than two years against fellow welterweight and TUF alum DaMarques “Darkness” Johnson Saturday August 4 at the Staples Center.

Josh Grispi also returns to the Octagon for the first time since June of 2011 that same night to face Pablo Garza. Once on the doorstep of a featherweight title berth, Grispi is looking to work his way up the ranks once more, but he will have to get past the durable Garza. Both fighters have the ability to end a fight in the blink of an eye.

In more 145-pound action in LA., Nam Phan will take on Cole Miller and Manvel Gamburyan will face Michihiro Omigawa in two must-see featherweight throwdowns.

Griggs Gets Mr. Wonderful for 205 Debut updated May 9
After losing to Travis Browne at UFC 145, heavyweight Strikeforce veteran Chad “Grave Digger” Griggs has verbally agreed to drop to the light heavyweight division. Welcoming him at 205 pounds will be Browne’s teammate, pedigreed wrestler Phil “Mr. Wonderful” Davis. The two have verbally agreed to meet at the UFC on FOX event in August.

Mitrione, Lauzon, Brits Added to August Card updated May 9
Two heavyweight bouts have been verbally agreed to for August 4 at the Staples Center. Englishmen Oli Thompson and Phil De Fries will clash in Los Angeles, while their countryman Rob “The Bear” Broughton will fight TUF standout Matt Mitrione.

update: A lightweight scrap between two always-entertaining fighters has been verbally agreed to, as Joe Lauzon and Terry Etim will test their slick submission skills against one another.

Darth vs. the Dragon, Heavyweights Heat Up August updated April 30
Coming off of back-to-back wins over Jason Brilz and Quinton Jackson, Ryan “Darth” Bader has verbally agreed to face former light heavyweight champion Lyoto “The Dragon” Machida at UFC on Fox August 4.

update: Two big guys coming off of big wins have also agreed to exchange that evening as heavyweight Ben Rothwell takes on Travis “Hapa” Browne. Rothwell earned the KO of the Night bonus while Browne scored Submission of the Night last week at UFC 145.

Lombard Draws Stann for First UFC Bout in August updated April 29
Following the recent signing of international star Hector Lombard to a UFC contract, the organization today announced that the former Cuban Olympian, who is currently sporting a 25 fight unbeaten streak in MMA, will make his Octagon debut this August in Los Angeles against middleweight contender Brian Stann.

A date and venue for the bout will be announced shortly.