Makoun made his Olympiacos debut, coming on as a substitute in the 67th minutes, in a their 1–0 loss to Marseille in the UEFA Champions League Group Stage march on 13 September 2011. Five days later on 18 September 2011, he made his league debut five days later, coming on as a substitute in the 69th minutes, in a 2–1 win over Skoda Xanthi. Since making his debut at Olympiacos, Makoun established himself in the first team, playing in the midfield position. It wasn't until on 5 November 2011 when he scored his first goal for Olympiacos against Aris in a 3–2 away win. However, in a follow up match against bitter rivals Panathinaikos, Makoun suffered a knee injury, resulting in his substitution and was that kept him out for six to eight weeks. It wasn't until on 4 January 2012 when he returned to the first team from injury, coming on as a second-half substitute, in a 1–0 win against Atromitos. A month later on 19 February 2012, Makoun scored his second goal for the club, in a 2–0 home win against Panionios He then played a role, assisting two goals in each two matches between 25 March 2012 and 1 April 2012 against Asteras Tripolis and Panetolikos (which a victory against them saw the club become the league champions for the second time in a row). Makoun started in the Greek Football Cup Final against Atromitos and played 82 minutes before being substituted, as Olympiacos won 2–1 after playing at extra time. Having made thirty appearances and scoring two times in all competitions, Makoun returned to Aston Villa after Olympiacos didn't have a budget to sign him on a permanent basis. He spoke about his time at Olympiacos, saying: "I think I've had a good season. I took a lot of time to participate, I won titles. It was a good experience in Greece, in a great team and a really impressive atmosphere. I am very happy with what the team has achieved and I personally. I always want to play well and win titles. Of course, along the way you can have your ups and downs. When you belong to Olympiakos, you always want to win, for the team you represent and its history."