Not sure, but you'd think it'd take him a long time to get back good enough for Pro MMA???
From that article link I posted:
"UFC heavyweight Frank Mir, who split his two fights with Lesnar, is already talking up a potential rubber match if Lesnar returns to MMA.“I think I would crush (Lesnar) standing up now,” Mir told The Fight Corner. “I think that on the ground and stuff, I’ve worked with (2x FILA World Champion) Ricky Lundell and stuff a lot and learned how to nullify the wrestling. I wrestled three rounds with Daniel Cormier who’s an Olympic level wrestler and he had a difficult time taking me down. I think that Lesnar would really have to throw caution to the wind and really rush through and I don’t think that he’s gotten any better at wanting to take punches.”
Brock Lesnar won't like that!!!