Panathinaikos, initially on loan, but with an option for the Greek club to sign him permanently. On 31 May 2017, his goal and overall positive performance, helped his club to succeed an away 3–2 win against rivals PAOK in the last matchday of the 2016–17 Playoffs depriving them of the possibility to participate in the UEFA Champions League third qualifying round. Return to AEK Athens On 29 June 2017, Klonaridis joined Super League side AEK Athens by signing a contract until June 2020. AEK paid €200,000 to acquire Klonaridis from Lens. On 8 August 2018, he scored before the break in a 1–1 away draw for UEFA Champions League Third qualifying round, 1st leg against Celtic. On 22 August 2018, he scored, slamming home the rebound from close range after Anastasios Bakasetas' snapshot had been parried by MOL Vidi's goalkeeper Ádám Kovácsik in a glorious 2–1 away win for UEFA Champions League Playoffs, 1st leg against MOL Vidi. On 16 September 2018, Klonaridis scored his first brace with the club in a 4–0 home win game against Panionios, as six minutes from full time with a brilliant piece of individual skill, skipping past the challenge of Luis Gustavo Dominques before firing a powerful shot beyond Panthers goalkeeper Filip Manojlović and at the last minute of the match scoring his second of the night, slotting home after good work from striker Marko Livaja. On 2 October 2018, he scored a brace in a 2–3 loss UEFA Champions League home game against Benfica. In both goals, he scored with a right footed shot from very close range after assisted by Niklas Hult and Marios Oikonomou respectively, but after the AEK forward missed a great chance for his hat-trick, Alfa Semedo's long-range strike won it for Benfica on the counterattack. He has become the team's first player in history to score twice in one single group match. On 22 January 2020, Klonaridis scored his first goal for the season, after a Hélder Lopes assist, in a 3–1 away win against Volos. The speedy 27-year-old has previously been plagued by injuries this season. The goal was Klonaridis’ first since 2 October 2018, when he scored twice in a 3–2 home defeat to Benfica in the UEFA Champions League group stage. On 1 March 2020, Klonaridis scored a stunning goal in stoppage time to salvage a thrilling 1–1 away draw for AEK against Panionios. On