And he believes Tierney deserves to be in the same conversation as that trio.
Arsenal are looking to bring the Scottish international to the Emirates this summer and, though they have failed with a £15 million bid, they are expected to return with an improved offer.
Forrest, for one, isn't surprised one bit by the Gunners' interest.
He told the Daily Record: “I’ve faced Alba, Vertonghen and Kolarov. There are a lot of top ones when you go into the Champions League or Europa League or are playing with Scotland.
“But Kieran’s right up there. You can see the way he bombs up and down how fit he is and he’s good defensively as well. He’s a great athlete.
“He’s been training with the first team for a good four years now so I’ve played against him a lot in training.
“Whether you are playing against him or he’s in your team, you can see the quality he’s got.
“When you go away with the Scotland team others players who play against him realise how good he is."