In the summer of 2005, Sonck had three of his ribs broken after a horrific tackle by Wilfred Bouma in a goalless, meaningless friendly between Borussia Mönchengladbach and PSV Eindhoven.

Sonck took six months to recover, marking his return to competitive football with a goal in a 3–1 defeat by Bayern Munich.

Sonck left Gladbach at the end of the 2006–07 season, joining Club Brugge on a year-long loan deal while Borussia Mönchengladbach began playing in the second tier of the Bundesliga.

on a free transfer having fallen out with manager Adrie Koster over contract negotiations and lack of first team action.

Sonck was released in the summer of 2012 and spent a few months unemployed before joining newly promoted Waasland-Beveren near the end of October 2012.