"There is a huge talent in him," Hart told the BBC. "I played against him when he was high on confidence at Shakhtar. They were a pretty average team, to be honest.
"We played well against them. But he was such a threat. He smashed two past me across the two legs. I was really excited when he signed in the Premier League.
"He's still young. Chelsea are a bit of a difficult club to shine in at the moment. If he is one of the wingers when they find their feet, I'm excited to see what he can do."