The 25-year-old striker has been in scintillating form this season to reportedly attract the attention of several top European sides, including Liverpool, Arsenal and Chelsea.
Olympiakos coach Jose Miguel Michel admitted last month that it would be hard to keep the Greece international, even though he had a deal with the club until the summer of 2016.
However, Mitroglou has now renewed his contract for the second time in a year, extending his stay at Olympiakos until 2017.
No further details were disclosed, but it is reported that the new deal removes the buyout clause from his previous contract, which was understood to be around €8million.
Any club interested in signing Mitroglou would now have to agree terms with Olympiakos.