Gaitan, 32, was a big name in Liga NOS between 2010 and 2016 for Benfica, scoring 41 goals in 251 appearances and winning ten trophies.
His performances in the Portuguese top flight led to Atletico Madrid paying €25m for him in 2016.
Since then, he has played in China with Dalian Yifang and for MLS outfit Chicago Fire.
Most recently he had a very brief spell in France with Lille, but made just four substitute appearances prior to the Coronavirus outbreak.
The winger has reportedly turned down offers from Spain to join Braga, who finished third in the league this season.
He was also linked with a return to Boca Juniors, where he began his career.
Gaitan has won 16 caps for Argentina in his career, most recently representing them in 2016.