Even though he has expressed harsh words towards Vitor Belfort in the past, Chael Sonnen is impressed by the UFC on FX 8 headliner and believes he is "almost unstoppable" when competing in the middleweight division.

"He's just as fast, he's just as accurate, he's just as intimidating, but he's a lot smaller - when he made his [UFC] debut he was heavyweight, then he came down to light heavyweight, won the championship over Randy Couture. Now he's down at middleweight. This guy is almost unstoppable. Outside of Anderson Silva, we haven't seen anybody that can beat him here. Really big test and I think finally mentally he's starting to believe in himself."

-- Former Ultimate Fighting Championship (UFC) light heavyweight and middleweight title challenger Chael Sonnen gives the hard sell on Vitor Belfort on FUEL TV's UFC on FX 8: "Belfort vs. Rockhold" weigh-in show, saying that he believes "The Phenom" is "almost unstoppable" at 185-pounds. Since dropping to the weight class in July 2008, Belfort has gone 4-1 including four (technical) knockout victories with the lone defeat coming to the top pound-for-pound fighter in mixed martial arts (MMA), longtime UFC champion Anderson Silva. At 36 years of age and with nearly 17 years of professional fighting experience under his belt, Belfort doesn't seem to be slowing down one bit and Sonnen is quite impressed by the Brazilian's longevity at the top of the sport.

Can Belfort keep it up when he faces former Strikeforce champion Luke Rockhold on Saturday night (May 18, 2013) in the main event of UFC on FX 8? Tune in and find out.

MMAmania.com will provide LIVE round-by-round, blow-by-blow coverage of the entire UFC on FX 8 fight card, starting with the Facebook "Prelims," which are scheduled to begin at 4:30 p.m. ET, right on through the FUEL TV-televised under card bouts at 6 p.m. ET and then main card action, which is slated to begin at 9 p.m. ET on FX channel.