Mallo, currently playing in Greece for Aris de Salonica, must pay the victim 1,000 euros ($1,100) plus interest, as well as being fined 10 euros a day for 20 months.
The defender committed the offence while captain of Celta Vigo during a visit to face Espanyol on April 24, 2019.
Mallo passed the Espanyol mascot, dressed as a parakeet, and "with the intention of satisfying his libidinous spirit and undermining her sexual liberty, put his hands under her costume and touched her breasts", said the court's sentence.
The woman was forced "to step back and push the defendant away with her right hand," continued the sentence.
The case was provisionally shelved in 2019 but after appeals by the defence and victim it was reopened.