Brock Lesnar agreed to a contract extension with WWE in January 2013 that was believed to be for another two years. His original contract was up after Wrestlemania 29 this year and had he not signed the extension, he would already be gone.
While speculation about Lesnar returning to UFC is unfounded, even if he was able to resume fighting from a health standpoint he would have to get out of his WWE contract. Lesnar is believed to be contractually bound to WWE through the entire year of 2014, into the first quarter of 2015.
Lesnar's new contract included a main event match at Wrestlemania XXX, which is currently believed to be against Undertaker. He is expected to appear on this week's episode of Monday Night Raw in Richmond, Virginia.