Klaas-Jan Huntelaar was Schalke's second choice target to strengthen their attack in the January transfer market.
Bild and Sky in Germany have reported that Schalke are eager to bring the 37-year-old striker back to the club to help boost their hopes of survival in the Bundesliga this season.
The Gelsenkirchen side are second bottom of the table with seven points from 15 matches, having picked up their first win last Saturday when they hammered four past Hoffenheim at home. Only Arminia Bielefeld, who are 15th, have scored fewer goals than Schalke.