United crashed out of the Champions League following their 2-1 defeat to Basel on Wednesday.
Keane said on ITV: "I think (going out) reflects what United have done in truth, they haven't scored enough goals and they haven't beaten Basle or Benfica.
"People have talked about the young players - you've had [Phil] Jones, [Chris] Smalling, [Ashley] Young coming in, everybody building them up but they've got a lot to do, it's a reality check for some.
"I'd be getting hold of some of those lads, saying 'you'd better buck up your ideas'. United got what they deserved tonight."
Keane also launched an stunning attack on English football and insists that a Spanish club will win the Champions League this season.
He said: "This is a reality check for these so-called brilliant English teams and people who think this is the best league in the world.
"Chelsea and Arsenal will be a handful, but I wouldn't look beyond the Spanish teams. They are sending messages to everyone."