The status of a heavyweight title unification bout between Brock Lesnar and Frank Mir scheduled for UFC 98 “Lesnar vs. Mir 2” on May 23 at the MGM Grand Garden Arena in Las Vegas remains uncertain as of early Saturday.

The UFC could make an official announcement regarding the headlining fight’s status, if necessary, as early as Saturday night during the UFC 96 pay-per-view, Sherdog.com has learned.

FiveOuncesofPain.com was the first to report on Friday that Mir had withdrawn from the rematch due to a back injury, citing multiple unidentified sources. MMAWeekly.com later posted that the fight had been cancelled because of a knee injury Mir sustained in training.

On Friday, Bodybuilding.com did a video interview with Mir, who is attending the Arnold Classic Sports Festival and Fitness Expo in Columbus, Ohio. When asked when the bout would be happening, Mir said, “Hopefully the summertime. It was May 23, but I needed to get some scope done to my knee, so I got it done immediately last week, and it would be rushing it to try to fight that soon ‘cause I can’t train for four to six weeks.”

Mir’s manager, Dean Albrecht, did not address questions regarding the bout’s rumored postponement.

When asked about Mir’s status, Albrecht told Sherdog.com via text that, “He’s gotta nurse his knee.”

Inquiries placed with two of Lesnar’s representatives were not answered.

UFC President Dana White told Yahoo Sports on Friday that he was unaware of Mir’s injury or the fight’s cancellation.

“I don’t know anything about it, so I honestly couldn’t tell you anything about it,” White told Yahoo Sports. “I’m not too worried about it now. If that were the situation, I’d know about it. I honestly don’t know right now. I haven’t talked to Frank and I haven’t talked to Lesnar, and if that’s the situation, I’m not going to make any statements until I talk to everybody.”

Mir (12-3) became the first man to finish Brazilian legend Antonio Rodrigo Nogueira at UFC 92 in December. The 29-year-old Brazilian jiu-jitsu black belt showcased improved boxing skills and conditioning, as he won the UFC interim heavyweight title from Nogueira with an impressive second-round stoppage and did what Fedor Emelianenko, Mirko "Cro Cop" Filipovic and Josh Barnett could not.

Voted Sherdog.com’s “Comeback Fighter of the Year” for 2008, Mir battled through a difficult rehabilitation following a motorcycle collision with a moving car in September 2004 that broke his femur bone.

It took nearly two years before he stepped back into the cage. A series of lackluster performances to Marcio Cruz, Dan Christison, and Brandon Vera followed. However, the 29-year-old turned his fortunes around in 2007 and has since rattled off three wins in a row, including his 90-second submission against Lesnar 13 months ago.

Lesnar (3-1) captured the heavyweight crown in just his fourth professional bout at UFC 91 in November, as he stopped hall of famer Randy Couture on second-round strikes. The former World Wrestling Entertainment superstar has won back-to-back bouts since his submission loss to Mir in his promotional debut at UFC 81 in February 2007. At 6-foot-2, 265 pounds, Lesnar has emerged as one of the sport’s most intimidating figures. Based at the Minnesota Martial Arts Academy, he leans on an impeccable amateur wrestling background inside the cage.

Other bouts booked for UFC 98 include a welterweight showdown between former champions Matt Hughes and Matt Serra, along with a lightweight tilt pairing former titleholder Sean Sherk with Frankie Edgar. The event will also likely feature the return of welterweight contender Josh Koscheck in a match with Team Quest veteran Chris Wilson.