2018 ScheduleAll times ET
Costa Rica international moves to the Serie A side on a permanent transfer for an undisclosed fee, Arsenal said on Friday.
A team-by-team guide to the new Serie A season as Cristiano Ronaldo makes the move to the Italian top flight.
Frosinone beat Palermo 2-0 in the second leg of their playoff final on Saturday to earn promotion back to Serie A after a two-year absence.
Hellas Verona sealed an immediate return to Serie A with a draw on the final day of the Serie B season on Thursday.
An investigation into match-fixing in Italy may be expanded to include fixtures from Serie A, according to a report in La Repubblica on Wednesday.
Unusual betting activity in the city of Frosinone before the Serie A defeat to Napoli has led to an investigation being opened.
"Remarks such as these gratuitously feed suspicion and cast a shadow over Italian football," said Frosinone president Maurizio Stirpe.
Inter Milan kept their slender hopes of securing a Champions League spot alive as they struggled to a 1-0 win at 10-man Frosinone in Serie A.
Juventus kept in touch with Serie A leaders Napoli ahead of next weekend's Scudetto showdown in Turin by beating Frosinone 2-0.