William Gallas is concerned by Kai Havertz's start at Arsenal, and feels his former club made a 'mistake' signing the Germany international this summer.
After three years at Chelsea which saw him win the Champions League and Club World Cup, Havertz joined Arsenal for £65m in July.
Havertz has featured regularly for Mikel Arteta's men in the opening weeks of the season, but has struggled to nail down a position in the side and only has one goal to his name so far - a penalty in a routine 4-0 win against Bournemouth.