Benfica's Angolan striker Pedro Mantorras was arrested

Reports quoting the police say that the player was detained on suspicion of carrying a false passport.

The player was returning from Switzerland, where Benfica had been holding a pre-season training camp.

The 22-year-old was questioned by border police for about an hour and then apparently spent the night behind bars before being released on Friday pending further investigations.

Benfica spokesman Antonio Cunha Vaz said border guards searched the baggage of all of Benfica's players on their arrival from Switzerland.

"They checked everything, the baggage of all players, the bags carrying footballs, the footballs themselves, everything," he said.

"When they checked passports some irregularities were detected in Pedro Mantorras' passport and he stayed at the airport to clarify the situation."

Border police are quoted as saying that they had found scratch marks over the validation date on the player's passport as well as other "signs of falsification".

Mantorras has had to sit on the sidelines nursing a serious knee injury since the start of the 2002/2003 season but doctors earlier this year finally approved his return to the pitch for Benfica.

Before his injury the 2001 African Young Footballer of the Year had sparked interest from various Italian and Spanish clubs, including Barcelona, and was tipped to become a star in European football.