Martínez made his first appearance since early last season on 6 April 2021 in the CONCACAF Champions League against Alajuelense, coming on as a 67th minute substitute in the 1–0 away victory. On 9 May 2021, Martínez scored his first goal of the season in a 1–1 draw against Inter Miami. In July 2021, after returning from Copa América, it was revealed by coach Gabriel Heinze that Martínez was training away from the team, with no specific reason given. Heinze was removed as Atlanta United's coach on 18 July and Martínez played his first match since returning on 21 July against FC Cincinnati. He came on as a substitute in the 1–1 draw.