Simpson is back at Old Trafford today for the first time since signing for Toon.
Ferguson said: "Danny's always been a terrific defender. That was his quality as a young kid here. He played a few games in the first team. We put him on loan to Newcastle to begin with and he did exceptionally well.
"They bought him eventually and he's been a consistent player for them. He's a regular, he's a very, very good defender and he's done well, the boy."