When Jose Mourinho was drawing up a list of targets ahead of the summer transfer window, one thing he looked at was Champions League experience.
Nemanja Matic had it. So did Victor Lindelof. But Romelu Lukaku didn't and so Alvaro Morata, who did, was also considered.
In the end, Mourinho picked Lukaku, deciding it was easier to make the transition from Premier League to Champions League than La Liga to Premier League.
After all, the main objective this season, whether Mourinho will admit it publicly or not, is to win the title.
Still, that will be briefly forgotten this week when the Champions League returns to Old Trafford for the first time since November 2015.
The talk will be about Mourinho's record -- two wins with Porto and Inter Milan plus eight semifinal appearances -- and whether or not United can win it.
The bookmakers think they can. United are among the favourites behind only Real Madrid, Paris Saint-Germain, Bayern Munich, Manchester City and Barcelona. You can get longer odds on Juventus, who have reached two of the last three finals.
It is perhaps to be expected that United are so well fancied despite failing to qualify in two of the past three seasons. Mourinho's history in the competition is part of it. So, too, the fact he has spent nearly £150 million to improve a team that won a European trophy last season.
But, then, in other ways it is curious. Not least because United's two main goal-scorers, Lukaku and Marcus Rashford, are yet to prove themselves in Europe's top club competition.
Rashford has never played a Champions League fixture. Lukaku's experience extends to a handful of qualifiers with Anderlecht when he was a teenager. Yet both will be expected to score the goals to get United out of a group that also includes Basel, Benfica and CSKA Moscow.
It might seem like a straightforward draw, but it has not escaped Mourinho's attention that United finished third in Group C behind Basel and Benfica in 2011 and failed to get out of a group that included CSKA Moscow in 2015.
It raises the question about whether Champions League experience matters. Paul Ince says it does. "It is highly unusual these days for a £75 million striker not to have had previous experience," the former United midfielder said of Lukaku.
"If he wants to be considered world class, this is the stage where he has to prove himself."
Sir Alex Ferguson, though, would probably tell you otherwise.
He spent £12.6 million on Dwight Yorke in 1998 despite the striker's previous European experience amounting to two goals in seven games for Aston Villa in the UEFA Cup.
But it didn't stop Yorke scoring eight goals in 11 games in his first season in the Champions League, including three in the knockout rounds, on his way to winning it in 1999.
Wayne Rooney had never played a European club fixture before scoring a hat trick for United against Fenerbahce in the Champions League on his debut. That said, he had just scored four goals for England at Euro 2004.
Rashford has already scored on his United debut, European debut, Premier League debut, League Cup debut and England debut. It would be no surprise to see him do it again on his Champions League debut.
The bookies don't think experience matters and Lukaku is among the favourites to score the most goals in this Champions League this season alongside Cristiano Ronaldo, Lionel Messi, Robert Lewandowski and Neymar.
The Belgian is a better bet, they reckon, than established Champions League strikers Sergio Aguero, Gonzalo Higuain and Karim Benzema.
But here lies the debate about Lukaku, in particular.
There is little doubt about his ability to score in volume. Detractors call it being a "flat-track bully". But it is his impact in the big games that draws the most attention. He scored 15 goals in 57 games against the Premier League's top six for West Brom and Everton -- almost a goal every four games.
You can argue that, with better players around him, that should change but we will not know for sure until United play Liverpool at Anfield on Oct. 14.
In Lukaku's defence, he has already scored against European champions Real Madrid in the Super Cup this season, albeit in a 2-1 defeat.
United's staff say Lukaku genuinely believes he will, one day, become the best striker in the world. But even he has admitted he will have to perform in the Champions League before everyone believes it.
"It's difficult to compare at the moment," he said. "They have the Champions League platform to show themselves. Those are the top games where I need to show people I belong to them too."
He is set to get his first chance this week.