The Serbian midfielder spent the last two seasons at Hertha, but Liverpool want to assess him this preseason before making a decision on his future.
And Preetz has admitted his club are monitoring the situation at Anfield.
"Unlike last year, it was Liverpool's declared wish that Marko should take part in much of the preparation there.
"Then there will certainly be a decision in England about Marko's immediate future: Will he be loaned out again? Is he for sale? Will he be part of the Liverpool team?
"That cannot be foreseen at the moment."