Arsenal have been granted a work permit for Villarreal defender Gabriel Paulista and are hoping to confirm his signing in the next 24 hours.
The La Liga club have said an agreement has been reached in principle for the £15m-rated 24-year-old.
Gunners striker Joel Campbell, 22, is moving the opposite way on loan, according to the Spanish club.
Arsenal boss Arsene Wenger has said the uncapped Brazilian has "good potential" and could adapt to English football.
Wenger confirmed on Thursday that the Premier League club were in talks over the signing of the centre-back, who joined Villarreal from Brazilian club Vitoria in 2013.
After the Gunners' 3-2 FA Cup win at Brighton on Sunday, Wenger added: "Paulista is a central defender but he can also play on the flanks.
"He is tall and pacy. He has a good chance to adapt to English football."
Campbell, who Villarreal claim will join on loan until the end of the season, signed for Arsenal in 2011 from Costa Rican club Deportivo Saprissa SAD.
He has since been loaned out to French club FC Lorient, Spanish side Real Betis and Greek outfit Olympiacos.
Campbell helped Costa Rica reach the quarter-finals of the World Cup in Brazil in 2014 and has made 10 appearances - without scoring a goal - for Arsenal this season.