Complex sentence: Mertens moved from the reserves of K.A.A. Gent to the first team of Cercle Brugge in the 2010--11 winter transfer window, at the recommendation of manager Bob Peeters, who had been his coach at the Gent reserves the previous season.
Split into simpler sentences: Mertens moved from the reserves of K.A.A. Gent to the first team of Cercle Brugge in the 2010--11 winter transfer window. Gregory Mertens signed for Cercle Brugge at the recommendation of Cercle Brugge manager Bob Peeters, who had been Mertens' coach at the Gent reserves the previous season.