The Blades boss has confirmed the two clubs have agreed a loan deal for the Greece international, but Robson hopes to convince Stelios to commit long-term at Bramall Lane.
Robson said: "We're taking talks further forward. At the moment we need to convince Stelios that Sheffield United is the right club for him to progress his career.
"He had a hernia operation and it's a four-week healing process - he had two weeks in Greece and is still over there at the moment.
"I'm trying to get in touch with Stelios to convince him that Sheffield United would be the right move for him."