Manchester United face the most demanding test of Ole Gunnar Solskjaer's interim reign when they face Tottenham at Wembley on Sunday.
And the Norwegian's No.2 Mike Phelan has identified what the Old Trafford giants must do to improve, despite making a perfect start under the club legend.
Solskjaer has won his first five matches since replacing the sacked Jose Mourinho last month - something only Sir Matt Busby has previously achieved as United manager.
But despite that impressive run of victories - and a return to the club's traditional attacking approach - Phelan accepts there is plenty of work still to do.
Solskjaer, 45, has overseen wins over Cardiff, Huddersfield, Bournemouth, Newcastle and Reading, but United only kept clean sheets in the latter two of those games.
Third-placed Spurs - 10 points and three Premier League places better off than United - will present a sterner test and, though Phelan says they will not 't alter their attacking intent, he acknowledges they must get better defensively.
"We're in a rich vein of form now. What we have asked them to do, the players have done," Sir Alex Ferguson's former deputy told Stadium Astro .
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"There are lots of areas of the game we can improve on. That's the beauty of it now. We can actually analyse the games that we have played and sometimes we have been fantastic going forward and a little bit sloppy defending.
"But the players now know both sides of the coin so we can work on that now and that will be our intention leading up to the Tottenham game because that will be a different test."
Phelan suggested United will be inspired by playing at Wembley - despite the challenge of taking on Tottenham at their temporary home.
"It's Wembley," he added. "I'm sure Manchester United players love Wembley.
"I think it's going to be a great football match and, obviously, Manchester United have to turn up and do what we're doing, and do more and I think we can do that."