Talks have been held between the two clubs while Grujic has since returned to pre-season training with Liverpool.
Warnock blasted the player's agent last week and accused him of trying to get more money elsewhere.
However, speaking after Friday night's 1-1 draw with Torquay, the Bluebirds boss admitted he is still confident a deal will be done.
Asked about signing Grujic, Warnock replied: "We are always optimistic - you've got to be at my age.
"It's one of those things. We were a bit thin on the ground tonight in that area without Aron Gunnarsson as well.
"We have to make sure we get someone in in that position."
Pressed on more additions, Warnock added: "We have a couple of new names mentioned today.
"There's always names that crop that will surprise you and you're like 'wow, i didn't realise he was available'."