 Lehtonen made his NHL debut in the Bruins penultimate regular season game in a 6-1 defeat to the Buffalo Sabres on 11 April 2009.While with Skellefteå on 28 February 2011, Lehtonen's NHL rights were traded by the Bruins along with Jeff Penner to the Minnesota Wild in exchange for Anton Khudobin.On 4 May 2011, Lehtonen was announced as the new player of KHL's Severstal Cherepovets.