Männilaan came through the youth system at FC Flora. He made his debut in the Meistriliiga on 16 May 2018, coming off the bench in a 2–1 win against FC Kuressaare. He scored his first goal in Meistriliiga later on in the same season in a 6–0 victory against Pärnu JK Vaprus.[2]
Männilaan spent the first half of the following season rehabbing from an ankle ligament tear. In spite of the injury, he was sent on loan to Holstein Kiel, a German team then playing in 2. Bundesliga, for the second half of the year. Männilaan was assigned to Holstein's under-19 team, making his debut in A-Junioren Bundesliga on 10 August 2019. He scored his first goal in the league on 8 December against FC Energie Cottbus U19. However, that game would also end up being his last for the team.[3][4]
In mid-2020, Männilaan returned to the Estonian Meistriliiga, this time being loaned from FC Flora to FC Kuressaare. He made his debut for the team on 17 July 2020. In his second game for the team, Männilaan scored 4 goals in an 18–0 home win against Anija JK in the national cup. He finished the 2020 Meistriliiga season with 4 goals and 2 assists. After finishing 9th in the league, Kuressaare ended their season with relegation games against Maardu Linnameeskond. With two goals against Maardu, Männilaan helped the team remain in Meistriliiga.[5]
In the following season, Männilaan continued at FC Kuressaare on loan. In his first full Meistriliiga season, Männilaan was the joint-7th best scorer in the league, scoring 11 goals and helping Kuressaare finish 7th in the league.[5]
Männilaan's loan at Kuressaare was also extended for the 2022 and 2023 Meistriliiga seasons. Kuressaare again improved their form in 2022, finishing the league season at 5th place. As of mid-2023, Männilaan was again among the top scorers of the league, having scored 7 goals in the first 25 games of the 2023 season.[6] In June 2024, Männilaan was chosen as FC Kuressaare's best player of the month by head coach Roman Kožuhhovski.[7]
On 8 January 2025, Männilaan signed for Gibraltar Premier Division club Lincoln Red Imps on an initial six-month contract with the option for a further year.[8]