They sit fifth from four games but take on Liverpool at Old Trafford on Saturday in the late 5.30pm kick off.
They qualified for the Champions League group stages after beating Bruges in the play-offs.
But former England captain Shearer reckons, having spent nearly a quarter of a billion on talent since arriving, it's time for the Dutchman to deliver on the pitch.
"I would argue Louis van Gaal cannot even afford to draw it," Shearer wrote in his column for the Sun.
"He has been asking for more time for his team to blend, for young players to develop etc. Time is up I'm afraid - the time is now.
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Should Van Gaal get more time?
"You cannot oversee the changes he has made, backed by hundreds of millions, and then claim you are a victim because it needs time to blend. It is your job to mould a side and I would suggest a year is plenty for a club of Manchester United's standing.
"You can get away with the dull, functional football Van Gaal is dishing up if you are getting results. But if you go back to the end of last season Van Gaal's league run over the last 10 games now stands at three wins, three draws and four defeats."
And Shearer admits he can't understand Van Gaal's dealings in the transfer market.
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