Compper made his TSG 1899 Hoffenheim debut on 1 February 2008, where he started the whole game in the centre–back position, in a 2–0 win over Wehen Wiesbaden. Ahead of the follow-up match against his former club, Borussia Mönchengladbach, on 10 February 2008, Compper made an interview with Bild, where he said he had no grudge on his departure from the club. He played the whole match against his former club, where he set up a goal for Demba Ba, in a 4–2 win. Compper quickly established himself in the first team, where he played in mostly at centre–back. He was also in the squad that won promotion to the Bundesliga after beating Greuther Fürth 5–0 in the last game of the season. At the end of the 2007–08 season that saw TSG 1899 Hoffenheim promoted to the Bundesliga, Compper had made a total of 19 appearances in all competitions.