Every footballer has his level.
Some reach theirs in the school playground. Others at schoolboy or county level. A select few are good enough to play professionally. Some in League Two, some in the Premier League.
The Champions League, especially the latter stages, is another level. Another step up.
And there's a danger that it's a step too far for Marouane Fellaini.
But those teams all have something in common. They are, in Premier League terms, average.
More than £27 million, the price David Moyes paid his former club last summer, should get you more than that.
Fellaini struggled against Manchester City and Liverpool at Old Trafford as both games ended in 3-0 defeats. And he looked out of his depth against Bayern Munich, Philipp Lahm, Bastian Schweinsteiger and Toni Kroos on Tuesday night.
For most of the Champions League quarter-final first leg, he looked lost. Like the overgrown, uncoordinated kid at a school disco, who's trying to copy what everyone else is doing on the dancefloor but still looks horribly out of place.
On a night that showed off the technical excellence of Lahm, Schweinsteiger, Kroos and Carrick, he stood out like a 6'4" bloke with an afro.
There were warning signs this summer.
If Moyes knew Fellaini was the man to solve United's problems in midfield, he would have arrived the day after Moyes on July 2.
That the deal was left to literally the last minute tells its own story.
So does the queue of clubs, or not as it happens, waiting to snap him up.
Moyes' only hope is that Fellaini comes good.
The 26-year-old's first season at Old Trafford has been disrupted by wrist and back injuries.
His start against Bayern was only his 14th for United and just his fourth in the Champions League this season. If he's not yet up to speed, it's understandable.
But if this is Fellaini's level—competent against the average teams, out of his depth against the good ones—then the United manager has got a problem.
He'll have spent nearly £30 million to solve an issue that will still be outstanding next summer. It will be another job on an already lengthy to-do list.
Even with the benefit of time, there's always a chance that Fellaini is not cut out for the level United want to compete at. Not cut out for the latter stages of a competition that involves the best teams in the world.
And, so far, he's done little to suggest otherwise.