The BBC reports that the 28-year-old, who claimed the IBF world welterweight title by beating Shawn Porter in California last month, is in hospital in Tenerife with injuries that are said to be "not life threatening".
The Daily Telegraph reports that Brook was stabbed in the leg and cut on one arm while on holiday with his partner, who is pregnant with their second child.
Brook has a perfect 33-0 record since turning professional 10 years ago, and after claiming the welterweight crown was looking forward to a potentially huge domestic superfight against Amir Khan next May - after which he was expected to earn a major match-up against the likes of Floyd Mayweather or Manny Pacquiao.
[BROOK EARNS RIGHT TO SUPER-FIGHT]
The incident in Tenerife - the details of which are not year clear - is, shockingly, the second time in his life that the Sheffield-born fighter has been stabbed.
In 2007, he was treated for wounds in his side and buttocks after an incident at a nightclub in his home city. Thankfully, he was able to return to action just six months later, and fans will be wishing him a similarly speedy and successful recovery this time.
It is the second incident to hit a British boxer in Spain this summer: former European champion Jamie Moore was kneecapped as he was shot five times in Marbella a month ago in what Spanish police believe was a case of mistaken identity.