In his pre-match programme notes, Ten Hag had called for his side to show fight and make amends for the 4-0 defeat they suffered against Crystal Palace last week.
But, for Keane, that fight was nowhere to be seen.
“You look at that last half an hour – the decision making, nobody digging anybody out, people making mistakes and falling over, and everyone just walking away, nobody putting demands on each other,” he added.
“That United team there – so bad.”
In isolation, a narrow loss to title-chasing Arsenal was arguably not a bad result for a side who started the day eighth and 29 points behind the Gunners.
But it was their 14th defeat of the season in the Premier League – more than any other side in the top half of the table – that leaves them in danger of no European football next term.
They have also lost nine games at Old Trafford this term – their joint-most at home in a season – and have conceded 82 goals in all competitions, which is their most since 1970-71.
“When you are losing games in the way Manchester United are at the minute there are going to be questions asked of the manager,” the club’s record goalscorer Wayne Rooney said on Sky Sports.
“But I think the players need to look at themselves. For some players it does look like they are just trying to reach the end of the season.
“If they are playing for Erik ten Hag I don’t think they are showing it very well.”
