Napoli have bought Slovak international midfielder Stanislav Lobotka from Celta Vigo, the two clubs announced on Wednesday.
Neither club revealed the transfer fee but the Spanish press estimated that it was 25 million euros.
Lobotka, who is 25, joined Celta in 2017 from Danish club Nordsjaelland. He has 18 caps for Slovakia.
Napoli are 11th in Serie A but have reached the last 16 of the Champions League and will face Barcelona.