He won the belt from Shawn Porter by  majority Brook vs Chaves Live Stream decision last August. The 29-year-old British star has since defended it successfully with victories over Jo Jo Dan and Frankie Gavin to push his career record to 35-0 with 24 knockouts.
Chaves started his career 22-0 before going 1-2-1 over his last four bouts. That's mostly due to an increased level of competition, though. He lost to Keith Thurman and Brandon Rios while earning a draw with Timothy Bradley. The only win during the stretch came against Juan Alberto Godoy.
Still, his competitiveness in those high-profile fights ensured he had the respect of the champion, as noted by of the International Business Times.
"Chaves is a rough, tough, durable fighter who is very dangerous," Brook said. "He's bringing something new to the table. He's coming off a draw to Tim Bradley, was ahead on the cards against Brandon Rios until he was disqualified and gave Keith Thurman a solid fight so we know what level he has mixed at and how good he is."
Hearn didn't provide any further details about the extent of Brook's rib injury. That said, the fact they are hoping to reschedule the fight within the next three months suggests it's not overly serious. He'll just have to avoid a setback once he begins ramping up his preparations again.
Brook certainly can't afford to enter the bout with any pre-existing injuries. Chaves brings a lot of power to the table with 19 knockouts out of 23 career wins. He's surely going to attack the ribs with some body shots early on to test the champion.
For now, however, Brook is focused on his recovery. So fans will be forced to wait a little longer for the hyped encounter.