Manager Frank Lampard has told the German he will not play regularly this season.
And according to the Mirror, Rudiger cannot go unless he agrees to a 12-month extension to his contract, which currently expires in 18 months.
Chelsea want to make sure the player does not leave on a free transfer shortly after he comes back from a season-long loan spell.
If Rudiger commits to the extension, he will likely go on loan before the deadline.
A permanent sale is not ruled out either, with Tottenham showing interest if they cannot sign Milan Skriniar from Inter Milan.
PSG have also shown an interest in the Germany international.