The boxer from Sheffield is in a stable condition according to his promoters Matchroom. No arrests have been made.
A spokeswoman for Spain's Guardia Civil said the 28-year-old was stabbed in the left leg at Golf del Sur in San Miguel de Abona and "lost a lot of blood".
Brook won the IBF welterweight title when he beat American Shawn Porter in California last month.
It is the second time Brook has been stabbed, after an incident in Sheffield in 2007.
Brook's win over Porter stretched his unbeaten professional record to 33 fights and he is being lined up for a fight against Amir Khan next - expected to take place on 6 December.
His trainer Dominic Ingle told BBC Look North: "We've been through a lot together, me and Kell, and receiving the news this morning hit me in the pit of my stomach. It's a sickening feeling.
"I think he's stable, his mum and dad's gone out today to see him in hospital.
"He's a fighter Kell, we don't know the extent of his injuries but whichever way, knowing Kell, he'll try and make that date [in December] if he can."
World boxing champion Kell Brook is in hospital in Tenerife after being stabbed in the leg while on holiday.