Pogba signed for United in August 2016 for a then world record fee of £89.3million.
The 26-year-old’s form in those three seasons has been up and down but this has not stopped him being linked with a move away from Old Trafford.
The latest reports suggest Real Madrid are preparing a bid in excess of £130million to lure the midfielder to the Bernabeu.
On the Weekend Sports Breakfast, Cascarino said that United should look to move the France World Cup winner on.
He said: “This August will be three years of Paul Pogba. How has he been in those three years? We’ve seen some really good highs. He’s had his moments but not consistent enough and not brilliant enough to be a player you want to build a team around.
“He’s 26-years-old. I, personally, would sell him. Why? You would get a fantastic fee for him that would enable you to build a team of other players that would contribute if not the same or more than Pogba can.
“I think United have had an alright Paul Pogba. No better than that. I think he’s had good moments. What would you give him out of 10 for his three year period? Seven at best.”