Osasuna sacked coach Luis Miguel Ramis and rehired Jagoba Arrasate as his replacement on Monday, following a 5-2 thrashing by Real Betis in La Liga this weekend.
The Pamplona side are 16th after eight games, with no wins in their last five matches.
Arrasate coached Osasuna from 2018 to 2024 before taking over at Mallorca, where he was sacked in February this year.
"The coach with the second most games at the helm in the club's history returns home to start a new project," said Osasuna in a statement.
Arrasate, who took Osasuna into the top flight in 2019, signed a contract until June 2029 and his first game is against promoted side Racing Santander on Sunday.
