Thordarson, who managed Gudjohnsen when Iceland's head coach at the turn of the century, recalled to The Sentinel: "I brought him in when he was only young after he'd had a difficult spell with ankle injuries.
"Unfortunately, he was out of my reach when I was Stoke manager. They were difficult times then.
"I think Eidur wants to prove a point and that is key," he said. "He wants to show everybody what he's capable of doing and still capable of doing.
"I think his international career will definitely kick on. He wasn't selected for these latest internationals because he didn't have a team.
"Mind you, I would still have picked him because even when he's not fully fit, he's still better than many players."