A fire on Friday left ten people dead and three people injured at Flamengo's training centre in Rio de Janeiro.
The state-of-the-art complex had undergone an expansion and opened two months ago, Reuters reported.
None of the victims has been identified but players aged between 14 and 17 are known to have used the dormitory.
"Flamengo is in mourning" the team posted on its Twitter account.More news: Apple gives education grant to United States teen for FaceTime bug find
Players were reportedly sleeping in their dorm when the fire broke out.
It was not known if any players were hurt in the blaze, although the club has accommodation for teenage players at the ground. The fire department have said that they can not yet discount the possibillty that they will find more bodies.
The best of those eventually play for Flamengo and several other teams across Brazil.
After years of financial difficulties, Flamengo last year spent 23 million reais ($6.2 million) to expand the Ninho do Urubu facilities.More news: House Panel Votes to Authorize Subpoena for Acting Attorney General
The Ninho do Urubu, or Vulture's Nest is so called because the club's symbol is a vulture.
Family members, friends and neighbors were gathering outside in hopes of getting information.
The Brazilian newspaper O Globo released pictures of the affected parts of the training ground on Friday morning.
Jefferson Rodrigues, who runs a small inn near the club, said he had reached a 15-year-old player he had befriended. "He lost his phone, and all of his things, but the important thing is he is alive". Instead, he went to a friend's house. "Today I woke up and heard this awful news".More news: Raptors getting Marc Gasol for Valanciunas, Wright, Miles, 2nd-rounder