Leicester City are closing on a deal for Croatia international Andrej Kramaric, with the striker waiting on a work permit before completing a move to the King Power Stadium.
Nigel Pearson is, however, being linked with several other forwards across Europe.
They also report that a formal approach for the Japanese frontman has been knocked back.
Mainz manager Christian Heidel has refused to reveal the identity of the interested party, but he has admitted to seeing an approach rebuffed.
He told Bild: “The risk is too great in this situation. If he goes, I am left with no striker.”
Okazaki has offered eight goals to the Mainz cause this season and is a valuable part of their first-team set-up.
He has helped them to 12th place in the Bundesliga standings, but an alarming run of form means they are now glancing over their shoulder.
The German top-flight is so tight that only three points separate them from the relegation spots.
They will be looking to the likes of Okazaki to help steer them clear of trouble, with their last nine games delivering no wins and only four points.