Atletico Madrid signed Almeria full-back Marc Pubill on Tuesday after missing out on Jesus Areso.
Osasuna right-back Areso joined Athletic Bilbao earlier on despite reports Atletico had agreed a deal for the Spaniard.
"Our club and Almeria have reached a deal, as long as (Pubill) passes his medical and signs his new contract," said Atletico in a statement.
Atletico did not state how much they will pay to sign the 22-year-old defender who was linked with a £13 million switch to Premier League side Wolves.
Areso came back to Athletic Bilbao after departing their reserve side in 2021 for Osasuna, with the 26-year-old's return costing the Basque side up to €12 million, according to Spanish reports.
"Athletic and Osasuna have reached a deal for the transfer of the fullback Jesus Areso, who signs for the red-and-whites until June 30, 2031," said Athletic in a statement.
Ernesto Valverde's Athletic finished fourth last season in LaLiga and managed to tie down winger Nico Williams earlier this summer despite interest from Barcelona.