The 23 years old Gelson Martins, joined Atletico as a free agent from Sporting since last July and has made only one league appearance for Diego Simeone’s side.
He will now play for Monaco who are fighting against relegation from Ligue 1, currently second bottom in the standings and three points from safety after losing 2-0 to Dijon on Saturday.
The club is also expected to confirm a loan deal for Chelsea forward Alvaro Morata, who passed a medical in the Spanish capital earlier on Sunday.
