Ten Hag was looking for his men to win the Manchester derby at Old Trafford to put down a marker of progress, but they came up badly short as Manchester City eased to victory.
Erling Haaland put Manchester City ahead from the penalty spot in the 26th minute, while his second goal in the 49th minute effectively killed off the game.
Phil Foden then put the gloss on the victory for the visitors by striking with just ten minutes left and it finished 3-0.
The result was comprehensive and Keys believes that Manchester United are frighteningly bad considering how much they have spent on players.
He also expects Ten Hag to shoulder none of the blame for the result.
“£400m later it’s scary how bad Utd are”, Keys wrote on X.
“Ten Hag said he had a plan to beat City today. Does anyone know what it was?
“For sure he’ll blame the players for not sticking to it.”
The result leaves Manchester United sitting in eighth in the Premier League table and having lost five of their ten league games so far this term.