The Bermeo-born 23-year-old travelled to Italy earlier in the week to finalise personal terms before the transfer was signed off on Wednesday. Athletic have not disclosed the fee, though Italian reports put the deal at around €4.5m fixed plus €1.5m in variables, with the Basque club also retaining a percentage of any future sale and a right of first refusal.
Gomez leaves having made 117 appearances and scored six goals across three seasons with the first team, and was part of the squad that won the 2024 Copa del Rey, coming off the bench in the penalty shootout final victory over Mallorca.
A product of the Lezama academy, Gomez had two spells in Athletic's youth system - joining as a boy before dropping out during his teenage years, then returning for the juvenile ranks after a stint with Danok Bat. He made his first-team debut under Ernesto Valverde against Real Madrid at San Mames in August 2023.
The club thanked Gomez for his commitment and dedication during his time in Bilbao and wished him well for the future, both personally and professionally, as he begins a new chapter in Serie A.
Udinese unveiled their new signing with a nod to his homeland, describing him as bringing "Basque grit, Spanish character and great versatility" to the club. Gomez has signed a contract running until 2031.
Athletic Club have also granted team-mate Unai Vencedor special permission this pre-season to resolve his own future, with the club aware that further departures could follow as Terzic reshapes the squad following his arrival from a two-year spell away from coaching.
The Basque club's pre-season preparations continue at Lezama, with Terzic working to integrate his ideas before Athletic's first competitive fixture of the new campaign next month.