He told The News: "Ben's only a young lad but you can see he's got plenty of ability to be at a club like Chelsea.
"Obviously, I saw lots of him training every day and playing in the same team as him and I cannot see any reason why he won't do well at Pompey. He's a very good finisher, a real poacher, and is lightening fast.
"That frightens the life out of defenders and can really open things up for your team-mates. I like the fact he's so willing to learn as well. He listens to what he has to do and then acts upon it.
"For a young lad that's really good. I have to say, it was a pleasure to play alongside him at the end of last season."