The Magpies slumped to their fourth defeat of the season on Saturday.
The Magpies lined up in an attacking 4-1-4-1 formation, and paid the price as the Hornets overran them in midfield and took the lead through two Odion Igahlo strikes.
“We will have to look at the game again,” said McClaren.
“We were at home and we needed to be positive so we put a team out there to be positive to go and win the game.
“All the way through that’s what we did. So much so it almost got us back in to the game but that’s (also) what got us into trouble in the first place.”
Colback was offered scant protection from the attack-minded midfield in front of him and could do little to prevent the Watford onslaught.
Newcastle were second best all over the pitch, and look in need of a major rethink if they are to get their season back on track.
McClaren’s experiment with his team’s set-up suggests a manager who is yet to work out his best XI, and even the system in which to utilise them.
It’s a worrying state of affairs six games into the season and with Chelsea and Manchester City up next in the Premier League, there’s every chance it will be eight games without a win come the 3rd October.