The champions arrive at the Lane on Saturday after suffering a disappointing 2-1 Champions League defeat at Spanish outfit Deportivo La Caruna on Tuesday.
United have yet to win away from Old Trafford in three Premiership and one Champions League game so far this season.
Yet Glenn insisted: "I don't see uncertainty in their performance.
"Whenever you play United, you know you are playing a quality team.
"You know you have to perform at nine out of 10. It's no good for us on Saturday playing seven out of 10, we'll get beat.
"Ipswich would have looked at their team sheet last week and thought 'this is a good time to play them' but they got beat 4-0.
"I still say that if we're 3-0 up with 20 minutes to go against United the game is not over. I saw them in the Charity Shield perform outstanding in the second half and the same happened at Newcastle, they were 3-1 down, came back and if Giggs scores they would have won that game.
"So I'm not going to fall into that trap of thinking it's a good time to play them because it might be the worst time to play them."
Glenn Hoddle says he won't fall into the trap of believing there is an 'uncertainty' in Manchester United's performances this season and now is a good time to play them.