For the 2019–20 season, Sancet was included in the main squad by manager Gaizka Garitano. He made his professional – and La Liga – debut on 16 August 2019, coming on as a second-half substitute for Óscar de Marcos in a 1–0 home win against FC Barcelona; on 27 June (his sixth league start), he scored his first goal in a 3–1 victory over RCD Mallorca, also at San Mamés. By December 2020, he had reached sufficient milestones to trigger a €150,000 development payment to Osasuna.