Castledine joined Boro from Chelsea in January, having spent the first half of last season impressing in League One with Huddersfield Town.
However, his first six months as a Boro player did not go to plan, with a succession of injury issues restricting him to just one Championship start for the club.
His problems were resolved before the end of last season, which meant he was able to start pre-season this summer completely injury-free.
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And after watching the midfielder round off his pre-season programme by scoring two goals in Saturday’s 3-3 draw with La Liga side Espanyol, Hellberg is looking forward to seeing what Castledine can deliver once the real action begins this weekend.
“He’s [Castledine] only started one game,” said the Boro boss. “It was a good game, we won 4-0 against Preston, and he had been a good substitute against Stoke the week before and scored as a sub against Bristol City.
“I think it was unlucky with him in terms of the injury, but he’s been taking the summer break and worked very hard, and we all know his big quality around the box in scoring goals.
“You can see the finish for the first one [against Espanyol] is a brilliant one, then the header for the second one is a good header.
“There’s a lot of potential in this boy, and he’s like a new player for us. He can play in a lot of positions, so he’s a very good player.”
Having completed their pre-season schedule, Boro play their first competitive fixture of the new season on Friday night when they host fellow Championship side Wrexham in the first round of the Carabao Cup.
