Whether it's UFC or WWE, Brock Lesnar just can't keep out of trouble.

The disgraced UFC star returned to the wrestling ring over the weekened with a bout against Randy Orton. Lesnar seemed to forget which format he was fighting, splitting open Orton's head with a series of elbow blows.

Yesterday, WWE announced that Lesnar has been fined US$500 for the attack. That will probably mean little to Lesner who earned a reported $US2.5 million purse for his UFC victory over Kiwi Mark Hunt in July.

Following the fight with Hunt, the UFC announced Lesnar tested positive in two rug tests leading up to UFC 200 - on July 9, fight day - to the same substance found in his previously-announced failed test 11 days earlier.