But none more so than Shinji Kagawa. Whether he's scored a hat-trick or spent an afternoon on the bench or in the stands, there's always a question about Kagawa.
A pack of Japanese journalists record his every move. They follow him to Stoke. They follow him to West Bromwich. If Kagawa's there, so are they. And usually asking questions.
It was no surprise then that while David Moyes was answering questions about the Champions League quarter-final with Bayern Munich in the Europa Suite at Old Trafford on Monday, it wasn't long before he was talking about Kagawa.
But the enquiry was particularly pertinent this time.
In five games against Bayern for Borussia Dortmund, Kagawa was never on the losing side. In the 2012 German Cup final, he scored Dortmund's first in a 5-2 victory. He likes playing against the German champions.
And it's something that's not lost on Moyes.
It's something which we seriously considered.
Shinji is a really important player for us, we like him a lot, he gives us something different and he is certainly in our thoughts for the game.
Manuel Neuer also got the Kagawa treatment as Bayern held their press conference in a hotel outside Manchester.
The Japanese midfielder might not always have found life easy since moving to the Premier League in the summer of 2012, but the Bundesliga clearly hasn't forgotten him 18 months after his departure.
We know he is a very good player. He has continued to develop over here. He has to adapt to the physical side of the game in England.
It has not always been easy and he has not always been in the starting 11 but he is an excellent and dangerous player.
The date with Bayern has coincided with Kagawa's own revival at United.
The 25-year-old hadn't started a game for two months before he was named in the team to play West Ham at Upton Park. In the three games since van Persie injured his knee against Olympiacos, Kagawa has started in the wins over West Ham and Aston Villa.
He was left on the bench for the 3-0 defeat to Manchester City.
There have been times this season when Kagawa looked certain to leave Old Trafford in the summer.
But in the last fortnight he has enjoyed renaissance. And where better to announce it than in a Champions League quarter-final against an old foe?
All quotes obtained firsthand.