On 15 December 2016, Manthatis scored the only goal in a Greek Cup preliminary round match against Sparti.
On 21 January 2017, he scored, as a substitute, his first Super League goal in a 2–0 home win game against Xanthi.
Playing primarily as a right-back, he quickly established himself as a key figure in the team that finished in second place in the 2021–22 season.
[7] In January 2023, AKFC loaned Manthatis to Finnish club Kotkan Työväen Palloilijat (KTP) in top-tier Veikkausliiga.
[8] Manthatis would make 17 total league and cup appearances for KTP with one goal and one assist, before being recalled by AKFC in July 2023.