He moved on to Granville of the CFA 2. He was a member of their team that progressed through nine rounds of the 2015–16 Coupe de France to reach the quarter-finals, in which they faced Ligue 1 "giants" Olympique Marseille. The game was goalless until the 50th minute when Michy Batshuayi scored; Lemonnier had a chance to tie the scores following a 69th-minute corner, but did not place his header sufficiently accurately. He and goalkeeper Jérémy Aymes were named as "Le Figaro" men of the match. He helped the team gain promotion to the CFA, and made 27 fourth-tier appearances in the 2016–17 season. Lemonnier chose to leave Granville at the end of the season. Those involved with the club were disappointed at his departure, and the media reported that it would much weaken the side. He signed for Le Mans, newly promoted from CFA 2 to the new fourth-tier Championnat National 2. He missed only one match as Le Mans finished as champions of their section and gained promotion to the third tier. He started 32 of a possible 34 matches in the 2018–19 Championnat National, and scored in two of five consecutive wins in the last five matches of the regular season that secured Le Mans a play-off place. Facing Gazélec Ajaccio, who finished 18th in Ligue 2, Le Mans lost the home leg by two goals to one. In the away leg, they took a 73rd-minute lead, but still trailed on the away goals rule. In the third of six minutes stoppage time, Lemonnier conceded a penalty. The attempt was saved, and in the 97th minute, Mamadou Soro scored with an overhead kick to confirm a third successive promotion for Le Mans. Lemonnier started Le Mans' opening match of the 2019–20 Ligue 2 season.