Warnock wants to bring Grujic back for a second spell at the club, but thinks the midfielder's agent is holding things up.
“It's a waiting game, but we won't wait forever," the 69-year-old told BBC Sport.
“I think his agent – as they do – probably thinks he is going to try and make more money somewhere else.
“Liverpool want him to come and I think it will be good for him. I think Marko does as well.
“We will see what happens by Friday this week. I never lose sleep over targets if I am honest. I always think it's their loss if they don't come."