A year later, Lamprou went on loan to Excelsior but returned to Feyenoord during the winter break after failing to establish himself in the first team at Woudestein.

"[5] On 19 May 2015, after his exceptional year with Willem II, the club's technical director Carlos Aalbers announced the permanent signing of the Greek international for the next two years: "Kostas fits into the play of Willem II and he has proved last season in the Eredivisie that he is a very good goalkeeper.

On 14 September 2015, in the fifth matchday of Eredivisie in an away game against his former club Feyenoord, he had a number of great saves but could ultimately not avoid a defeat.

The 26-year-old goalkeeper signed from Willem II, after two excellent seasons with them as a free transfer, even though he knew that he started as a third option.

[10] In the beginning of the season he played for Jong Ajax, and on 25 October 2017 he made his debut with the first team in a 4–1 away win KNVB game against De Dijk.

[11] Eventually, on 6 May 2018, the Greek goalie was finally handed his Eredivisie debut with Ajax and by saving five Excelsior shots he guided his team to a 2–1 away win, sealing UEFA Champions League participation for the following season.

[13] On 16 July 2019, after two years with Ajax, Lamprou signed a one-year contract with another Dutch club Vitesse for an undisclosed fee.

[16] Lamprou returned to Willem II on 12 June 2022, signing a two-year contract with the recently relegated Eerste Divisie side.

[19] Lamprou's consistency meant his first international call up in October 2012 from Fernando Santos, the coach of Greece national football team.