Sir Alex Ferguson has warned Manchester United face a battle to prise Eric Dier away from Tottenham.
Teddy Sheringham, Dimitar Berbatov and Michael Carrick all made the switch down the years.
But getting deals over the line has proved tricky at Old Trafford, largely down to Spurs chairman Daniel Levy.
Ferguson has outlined how challenging reaching agreements with Spurs can be, especially from the Carrick saga in 2006.
"I must say negotiations were very difficult and went on for ages," Ferguson told MUTV. "I always remember I thought it was done and David Gill phoned me on the golf course to say they want more.
"Typical Daniel Levy!
“It was very hard to negotiate but, at the end of the day, we got it through and, ever since he (Carrick) joined us, he's had a fantastic career."