Lehtonen, 26, appeared in 60 games with Jokerit (KHL) during the 2019-20 season and registered 49 points (17 goals, 32 assists), which led all KHL defencemen. He represented Jokerit at the 2020 KHL All-Star Game and was named KHL Defenceman of the Month in three consecutive months from November to January. He had a goal and three assists in six KHL playoff games prior to the cancellation of the season. Before joining Jokerit, Lehtonen won an SHL title in 2016-17 as a member of HV71 and captured a Liiga bronze medal in 2017-18 with Tappara.