The 25-year-old joined the Cottagers for £11m from Olympiakos at the end of January but only made his first start for the club in Saturday's 3-1 defeat at fellow strugglers Cardiff City.
Mitroglou, who had previously featured for just 30 minutes in a Fulham shirt, played for 90 minutes against Cardiff but struggled to make a real impact.
Magath acknowledged after the game that the Greece international, who scored 21 goals for Olympiakos this season before his departure, is not used to a survival battle.
"Mitroglou is a player who is not used to a relegation fight," said the German.
"He comes from the best club in Greece, who was better than every other in their league, so he is only used to scoring. That is his strength.
"Here in the Premier League, the best league in the world, he is not used to it. Unfortunately he has some opportunities but at the moment he is not in the situation to score."