As confirmed in a statement on Los Rojiblancos' official club website, the 2017/18 La Liga runners-up have achieved a preliminary agreement for the transfer of the 22-year-old winger, which will see the France international link up with his compatriot Antoine Griezmann next season.
In their statement confirming their acquisition of Lemar, Atletico wrote: "Atletico de Madrid and AS Monaco has achieved a preliminary agreement over the transfer of Thomas Lemar to our club. Over the next days, both clubs will work to close the agreement for the definitive transfer.
"The French international is with his national team in Russia to play the 2018 FIFA World Cup that will take place on Thursday, 14th of July. Lemar, at 22-years-old and 1.70 cm of height, performs as a left winger.
"Lemar rose to Caen’s first team in the 2013-2014 season, playing 9 games. It was in the next season... when the winger was consolidated, playing 26 official games and scoring one goal.
"AS Monaco became the owner of his services at the end of the season and his debut with AS Monaco in the 2015-16 season confirmed the bet made by the team, due to the fact Thomas Lemar played 34 games between the whole competitions, scoring 5 goals and giving 5 assists.
"The season 2016-17 supposed the definitive step for the French international. Lemar participated in 55 official games, he scored 14 goals and gave 17 assists to his teammates. His contribution was key in the great season by AS Monaco, who achieved the semi-finals of the Champions League, in which the winger played 12 games, plus another 4 games in the previous rounds, scoring 2 goals and giving 6 assists, and conquered Ligue 1.
"In the last season, Lemar has continued showing his quality in the 38 official games played, in which he scored 3 goals and gave 10 assists to his teammates.
Lemar made his debut with the French National Team at the age of 21, on November 15th, 2016 against Ivory Coast. In total, he has played 12 games with Les Bleus, in which he has scored three goals, two of them in the qualification games for 2018 FIFA World Cup Russia.