Newcastle owner Mike Ashley for not improving the squad since last season’s heroics, which saw the Magpies finish fifth.
The English tycoon spent £8.1million in the summer to bringing in Vurnon Anita, Gael Bigirimana, Curtis Good and Romain Amalfitano (on a free).
Of the four signings, only Anita has managed to establish himself in the Toon’s starting line-up, and former Newcastle marksman Shearer says Ashley should have spent more money in order to keep challenging up at the top of the Premier League table.
“Newcastle missed a huge opportunity in the summer,” Shearer told The Sun.
“Having punched above their weight last season and almost made it into the top four, this was the time to spend.
“The club was up and running again after so many years mired in uncertainty.
“There was once again a feel-good factor and even Mike Ashley was enjoying it.
“But he needed to put his hand in his pocket and strengthen with two or three quality players.”
And Shearer feels his former club should have been able to compete with Tottenham in the transfer window, despite the fact that Andre Villas-Boas’ side were far more active during the summer months.
“It’s up to Ashley how much he spends — but just look at what Spurs did.
“They pipped Newcastle to fourth place and went out and spent £57million on six players. Newcastle spent £8.1m on three and got a fourth in on a free.”
Newcastle are 15th, just two points above the relegation zone. Saturday’s defeat to Manchester City means the club have won just one of their last ten games in all competitions.