His team travel to City on Saturday afternoon to take on a side that have won all three of their Premier League games this season, with their last result being a 5-1 thrashing of Tottenham at White Hart Lane in which striker Edin Dzeko scored four times.
"That team is now near enough unplayable when they go forward. They were a joy to watch against Spurs," Martinez told The Sun.
The Latics are currently unbeaten so far this season and find themselves in eighth position in the Premier League, but Martinez feels his team are up against possibly the best attack in the game.
"It's as good as it gets in world football, never mind in the Premier League," he said.