Ozil quit Germany citing racism after the World Cup.
Mertesacker said "no-one did a good job" dealing with the situation.
"Some players decided to retire in their own fashion," said Mertesacker. "In Mesut's case, it wasn't possible.
"I feel sad about the football association and Mesut and that they didn't find a way to go out on good terms.
"Who is the next Mesut Ozil? Who can step up and take us up to the Frances of this world, who overtook us when we were feeling complacent?"