Hart will sit out his third game on Tuesday night when Costel Pantimilon plays in City's Champions League encounter with CSKA Moscow at the Etihad Stadium.
With Fraser Forster likely to get his England chance in this month's friendly double-header against Chile and Germany, Hart is under pressure with both club and country.
But Manchester United's De Gea, who had to overcome his own troubles before sealing his status as one of the Premier League's top goalkeepers, is certain Hart will not be out of the limelight for long.
"Joe Hart is a great keeper," he said.
"It's very complicated to play at the top level and never to make mistakes.
"I am sure he will work very hard to go back into the first 11 and sooner or later he will make it."