Zarate is currently spending time on loan in Argentina at Velez Sarsfield. He is enjoying his football there, but believes there is unfinished business in Europe.
"I made a mistake in leaving Lazio at the time. I regretted it later," he told Radio Incontro Olympia.
"Going back? I think it's impossible.
"I'd love to go back and play in the team under Simone [Inzaghi], but we must also see if the coach wants me. It would be a dream.