Tselios began his career at the infrastructure segments of AEK Athens, and made his senior debut against Pannaxiakos on the last matchday of the 2013–14 Gamma Ethniki season.
He played for AEK's U−20 during the club's short tenure in the Football League and eventually made his Superleague debut in 26 November 2016, as a late substitute for Patito Rodríguez in a 3−0 home win vs. Platanias.
[1] At the start of the 2017–18 season, Tselios moved to fellow Superleague side Lamia on a one-year loan deal in order to get more playing time.
[5] His performances with the club made Ergotelis officials request an extension to his loan from AEK, therefore securing Tselios' services until the end of the 2018−19 season.
Having proven himself to be an invaluable asset for Ergotelis' style of play, the club's administration pushed for his acquisition via transfer from AEK.