The 25-year-old signed from Bayer Leverkusen in May 2012 but has only made 13 appearances and scored one goal since his move, making it difficult to earn an international call-up.
Hitzfeld hopes Derdiyok, whose current contract runs out in 2016, can find a new club before the current transfer window closes at the end of the month.
He told the Bild newspaper: "He should be looking for a club where he plays again. I need players that are regularly used in their clubs.
"This is currently not the case for Eren. The title chances of the national team decline if he, by the end of the transfer window, has not found a new club.
"He needs match practice, it is also an issue for the national team once again. Otherwise it becomes difficult."