Sir Alex Ferguson advised Jurgen Klopp that "strong management is crucial" when Philippe Coutinho handed in a transfer request in 2018.
Liverpool had publicly announced that Coutinho would not be leaving when Barcelona made three sizable bids for the midfielder two years ago.
But the Brazil international wasn't taking no for an answer and responded by handing in a transfer request via email to push through a £142million move in January.
Legendary Manchester United boss Ferguson experienced everything during his 39-year career in management, and was asked for his thoughts on the saga while at an UEFA Elite Coaches Forum in Nyon, Switzerland back in 2018.
Ferguson responded: "I think strong management is crucial in this situation.
Part of your job as a coach also is to educate your players' character so they have a responsibility to what they're doing.
"Obviously, in some cases, that is changing a bit. It's disappointing because I'm sure that, in the case of Liverpool, they did a very good job in making Coutinho the player he is today.
"So, it's a bit disappointing but you have to deal with it and the transfer window doesn't help in that situation.
"If it closed in July, Coutinho would have continued playing and it would have been gone. The matter would have been over.
"The recommendation we look at is to close the window before the season starts, so everyone knows which players they've got and aren't waiting to see what the first results are going to be."
