Hamza's contract with Mainz has been terminated by mutual consent on Sunday, and now is able to join any other club as a free agent.
The former Zamalek striker signed a two-year deal with Mainz on a free transfer, but he wasn't called up in nine successive league games.
He made one official appearance with Mainz in the Cup defeat against Lubeck in July.
Two days after Hamza's contract was rescinded, Heidel stated that he didn't get the chance to see the former Egypt man in action before the deal went through.
"Personally, (former Mainz coach Jorn) Andersen and I have never seen him," Heidel was quoted by Bild as saying.
"His skills are indeed indisputable, but he has never really acclimatized here."
Heidel also referred that Hamza's contract was terminated after the 27-year-old didn't show up at the club for two weeks.