Portuguese media reported that dozens of people stormed the Alcochete site, trashing buildings and even assaulting some of the players and staff.

Pictures have circulated of striker Bas Dost with several cuts to his head, although it is not clear when the images were taken.

Fans were also pictured protesting against the violence on Wednesday (AEST), showing their solidarity with the club.

The alleged incident took place just two days after a 2-1 defeat to Maritimo, a result that meant Sporting missed out on a UEFA Champions League place to Benfica.

A statement published via the club's Facebook page read: "Sporting Club de Portugal vehemently condemns the events registered today at the Academia Sporting.

"We cannot, in any way, agree with acts of vandalism and aggression towards players, coaches and staff in professional football, nor with attitudes that configure with the practice of crime that in no way honours or ennobles Sporting Clube de Portugal.

"Sporting is not this, and Sporting cannot be this.

"We will make every effort to establish the full responsibility for what has happened and we will not fail to demand punishment of those who acted in this absolutely pitiful way."

Tensions have been mounting at the Lisbon club in recent weeks amid poor results and an apparent conflict between the squad and club president Bruno de Carvalho.

In April, De Carvalho claimed he was suspending 19 of the first-team players after Sporting's UEFA Europa League exit at the hands of Atletico Madrid, although he later appeared to back down.

There have also been rumours he suspended boss Jorge Jesus and his coaching staff on Tuesday (AEST), with senior players reportedly threatening to boycott Monday's (AEST) Taca de Portugal final out of solidarity with their coach.