Lisbon - A 50-strong gang of hooded men brutally attacked Sporting Lisbon players and officials at training on Tuesday leaving the club in shock and casting doubt over their participation in Sunday's Cup final.

Wearing t-shirts bearing the club's logo the gang broke into Sporting's training ground and went on the rampage, terrorising players and personnel and vandalising dressing rooms.

Sporting's Dutch international Bas Dost, the club's top scorer this season, required stitches to his neck. A photograph of his bloodied face appeared on social media.

"It was a distressing situation and we are all shocked," the striker told Dutch news website Algemeen Dagblad.

Argentina international Marcos Acuna and Croatia's Josip Misic were also assaulted in the raid on Sporting's Alcochete training base in the Lisbon suburbs.

The team are meeting their player's union on Wednesday to discuss their reaction which according to domestic media could see them refuse to play in Sunday's Cup final against Desportivo das Aves.

Another option on the table is ending their contracts with the club.

The horrific incident left Portugal's President Marcelo Rebelo de Sousa "worried by the image this projects of Portugal to the world".

He added: "I'm concerned as Portugal is a power in professional football, and I'm worried about the seriousness of what's happened."

Portuguese police have made 21 arrests, according to the government.

Several hundred Sporting fans made their way to the team's Alvalde stadium on Tuesday night to lend their support to their stricken team's players and management.

Supporters group 'Juventude Leonina' issued a statement on social media strongly condemning the attack.

"The Juventude Leonina numbers more than 7,000 fans. It deeply regrets what happened and disassociates itself from these events."