The 24-year-old played no part in Sporting's 2-1 Segunda Division win at Numancia at the weekend as negotiations with Celtic gathered pace.
And Sporting's manager, Abelardo Fernandez, admitted that he is planning for a future without the talented hitman.
"Stefan is no longer part of my plans," Fernandez told reporters in Spain.
"His transfer is a done deal and because we don't want to endanger his move, he is not training with the players anymore."
The fee is reportedly set to be around the £3million mark, and Scepovic could be in the Hoops squad for Sunday's Scottish Premiership clash at Dundee.