[2] On 16 September 2020, Mannila was named the manager of Veikkausliiga club Rovaniemen Palloseura (RoPS), replacing sacked Vesa Tauriainen.
Next season Mannila led RoPS to finish 2nd in Ykkönen and qualify for the Veikkausliiga promotion play-offs, eventually falling short to AC Oulu.
Later RoPS were demoted to the third-tier Kakkonen for the 2022 season due to financial problems, and Mannila decided to leave the club.
[4] He managed to keep Lahti in the league, but couldn't change the club's direction in the 2023 season,[5] and eventually Mannila was dismissed on 31 August 2023.
[6] On 12 September 2024, Mannila was named a head coach of Ykkönen club Oulun Luistinseura (OLS), the reserve team of AC Oulu.