Brock Lesnar's prospective move back to UFC just took an unexpected hit.

The former UFC Heavyweight Champion was widely expected to return to MMA when his current deal with WWE expires after Wrestlemania 31 but according to veteran wrestling broadcaster Jim Ross, Lesnar isn't going anywhere:

"Sources are saying that it looks more promising that Brock Lesnar could well stay with WWE past WrestleMania due to concerns over long-term health effects of competing in MMA, specifically concussion-oriented issues later in one's life."

Lesnar, now 37-years-old, boasts a 4-3 record in UFC and retired after his last fight – a controversial defeat to Alistair Overeem – citing ongoing difficulties with diverticulitis.

Dana White said Brock Lesnar is interested in fighting again.

As recently as November 2014, UFC president White was quoted as saying:

"Brock Lesnar's under contract with the WWE. We have a great relationship with him. He's healthy and he has said that he's interested in fighting again. We'll see what happens."

 Lesnar made his WWE debut in 2002 and returned to the company in 2012. He's the current WWE World Heavyweight Champion and is slated to headline Wrestlemania 31 on March 29th.

[via Bleacher Report]