LaLiga has been suspended since March but has been given the green light to return from the week commencing 9 June (AEST), though all games will be played behind closed doors.
Leganes is based in Madrid, which has seen more than 67,000 cases of COVID-19 and just shy of 9,000 deaths as a result.
Due to the impact of the virus, Leganes has made all 2019-2020 season tickets valid for 2020-2021 in addition.
"Given the impossibility of playing the remaining matches of the 2019-20 season with open doors due to the effects of COVID-19, Leganes will compensate its subscribers by validating the current subscriptions for LaLiga matches of the 2020-21 campaign," read a club statement.
"The club, aware of the social reality that our city is experiencing, one of the hardest hit in all of Spain in terms of the level of deceased and infected ... wants, in this way, to be sensitive with all its existing season-ticket holders."
Getafe, which is also based in Madrid, made its season tickets for this campaign valid for the entirety of 2020-21 too.
Leganes sit 19th in LaLiga, three points adrift of safety with 11 games remaining.