The club said Cuellar was taken to hospital after the incident at the Ciutat Esportiva Antonio Asensio, also known as Son Bibiloni, before the squad's scheduled training session under manager Luis Garcia ahead of Sunday's Spanish second division match against Girona.
Despite the alarm caused by the accident, Mallorca said the keeper was recovering well, as doctors monitored his condition and ruled out further complications.
"This morning, Ivan 'Pichu' Cuellar suffered a serious head injury after a large structure, which formed part of the decor in the dining room at the Ciutat Esportiva collapsed," the club said in a statement.
"The player has been taken to hospital for treatment and will remain under observation for the next 24 hours."
Cuellar's injury leaves Garcia short of options in goal, with Lucas Bergstrom on international duty with Finland, leaving Arnau Tenas as the only one first-team keeper available.