Arsenal goalkeeper Petr Cech says that American Gedion Zelalem has great potential and has a chance to make the first team. SAN JOSE, Calif. -- Arsenal goalkeeper Petr Cech called the injury to Per Mertesacker "a big blow" and is calling on the likes of Calum Chambers, Rob Holding and Gabriel Paulista to pick up the slack. Mertesacker injured his knee in training and didn't accompany the club on their U.S.