Matmour made his Borussia Mönchengladbach debut, where he started and played 61 minutes before coming off as a substitute, in an 8–1 win over VfB Fichte Bielefeld in the first round of DFB-Pokal. A week later, on 17 August 2008, Matmour made his league debut for the club, starting the whole game, in a 3–1 loss against VfB Stuttgart in the opening game of the season. Two weeks later, on 30 August 2008, he scored his first goal for Borussia Mönchengladbach, in a 3–2 win over Werder Bremen. Since joining the club, Matmour quickly established himself in the starting eleven for the side. Despite receiving criticism for his lack of goal scoring form, he later scored two more goals for the club as the season progressed and they went on to finish 15th place in the league. Despite missing out one game during the 2008–09 season, Matmour was ever present in the league, as he went on to make 35 appearances and scoring once in all competitions. Matmour finished his first season at Borussia Mönchengladbach, making 35 appearances (34 in the league) and scoring 3 times in all competitions.