Alan Shearer said he was "staggered" that Newcastle allowed Andy Carroll to leave for Liverpool without bringing in anyone as a replacement.
Carroll, 22, joined Liverpool late on Monday night for £35million, a British transfer record that was quickly broken when the Merseysiders sold Fernando Torres to Chelsea for a fee believed to be around £50million.
And Shearer, Newcastle's record goalscorer, hopes that the Magpies' failure to reinvest any of the £35million in a replacement for the England striker does not come back to haunt them.
"I'm staggered just like the rest of Newcastle fans," he told BBC Five Live: "I am surprised at how quickly it came along and it's an astonishing amount for a young guy with huge potential.
"It's all right selling your best player, but not getting anyone in to replace him is staggering.
"People are saying that Liverpool have sold Torres, but they have got two guys in for over £50million to replace him. I just hope Newcastle invest some of the £35million in new players at the end of the season.
"I am disappointed as he is Newcastle's best player and their best hope of being successful this season and getting a Europe League place.
"They would have just been happy to avoid relegation at the start of the season but, mainly because of him, they had a chance of a Europa spot."
But Shearer believes that Carroll will only get better while working with Liverpool manager Kenny Dalglish.
"He is a huge loss, he has carried Newcastle at times this season. There are not many players like him," said Shearer.
He is big, strong, very good in the air and has a good left foot. You get that ball in the box and there aren't many that could stop him, but he will be a tremendous asset to Liverpool.
"Having worked with Kenny Dalglish I can tell you he is not only a great man, but a great manager. If anyone can get the best out of him then Kenny will.
"To work with one of the greatest football figures of the last two decades, I know he will learn the tricks of the trade from him and improve."
Carroll was reported in Tuesday's Daily Star to have sent texts to Steve Wraith, editor of the Toon Talk fanzine, claiming he felt he had being forced out of the club.
One of them reads: "Gutted to be leaving but I was kind of pushed out the door," with another one adding, "Gutted to be leaving my home club but I was practically told to go. Don't want to leave, that's why I signed a five-year deal."
Newcastle were not commenting on the texts today but Shearer said: "I wouldn't be surprised if he did not want to leave. I know he handed in a transfer request late in the day but I am not sure he wanted to leave."
