Victor Lindelof is the man in question, with Derby County manager Gary Rowett today telling 'Sky Sports' that he turned down the chance to sign the Swede from Benfica back when he was in charge at Birmingham.
"About two or three years ago when we first went into Birmingham an agent called us and said we are trying to get some of our younger players out to expose them to different levels," explained Rowett.
"We had a look at him (Lindelof) and put it to some of the staff, but it was ironic because they felt he wasn't probably quite tough enough.
"Then suddenly he's been touted around at £20m or £30m. So I think we made a mistake."
Lindelof also went on trial with Stoke City early in his career and came close to signing for Middlesbrough on no less than three occasions two years ago, with the Teessiders going as far as to book a private jet for the centre-back to make the flight to the North East to sign on the dotted line.
In the end, none of those deals came to fruition and in the height of an injury crisis, Lindelof was thown into the Benfica first team. He didn't look back, senior Sweden honours soon followed and after just 48 league appearances for the Portuguese side, the 23-year-old made the move to Old Trafford this summer for a fee in the region of £39.5m.
What could have been, hey Victor?