The Newcastle United legend wants a response after the West Ham United loss.
The Magpies are yet to register a win this season, five games into the Premier League campaign, and Shearer feels there will be a sense of restlessness on Tyneside if Watford aren't beaten on Saturday afternoon.
Indeed, the former Newcastle striker believes supporters won't hesitate to show their anger if all three points aren't claimed against the Hornets, with there already being huge pressure on Steve McClaren's men.
Shearer told Coral: "The pressure is really on when they play Watford, but you just never know with Newcastle. I watched them against Arsenal and they went down to ten men but still showed a lot of courage and fight.
"What I do know is that they definitely need three points against Watford. If they don’t, then I am pretty sure you will hear the Newcastle fans show their anger."
Newcastle fans will no doubt be familiar with the two sides of an argument every struggling new manager faces.
To call McClaren struggling after just five games may be harsh but the Magpies certainly haven't looked close to registering their first win at any point.
Hence the two different camps: those calling for him to get time and those disappointed the same flaws of last season's Newcastle team have carried on this term.
Beating Watford, as Shearer suggests, really is a must.