After missing out on Thiago Alcantara and Cesc Fabregas last summer, Moyes decided to boost his midfield ranks by signing Fellaini from Everton.
A few eyebrows were raised at Fellaini's price tag - especially when the midfielder was available for £4million less earlier that summer - but having worked with the Belgian for five years at Everton, Moyes was convinced he had the right man.
However, the reality is that Fellaini has struggled to live up to expectations since his move to Old Trafford.
The 26-year-old scored 32 goals for Everton, but he is yet to find the net at United while some of his passing displays have been forgettable.
Spanish newspaper AS was so unimpressed by Fellaini's performance in Tuesday's 1-1 draw against Bayern Munich that it did not deem the tall midfielder worthy of a mark out of 10 in their match report.
Like Fellaini, Moyes has found the switch from Goodison Park to Old Trafford tough, but the United boss is sure the 6ft 4in midfielder is starting to show his worth.
"It's not an easy move coming to Manchester United, as I can tell you," the United manager said.
"For Marouane, I think it's proved equally as difficult, but I have to say I think he has done a lot of good things and he has improved.
"I actually thought Marouane got better as the game went on (against Bayern).
"We needed him and I thought he played very well.
"He did well in the Villa game too. I think he is getting much closer to scoring.
"We bought Marouane Fellaini not to play every single game in the Premier League. We have bought him for several games. He did a great job at West Ham, against Aston Villa and against Bayern."
After a season full of disappointments, Tuesday's 1-1 draw against the reigning European champions was an uplifting experience for Moyes and his players.
Nemanja Vidic put United ahead in the second half and had it not been for a couple of missed chances, the Red Devils could have come away with a highly creditable win.
Moyes, conscious of the fact that there have been many false dawns this season, is reluctant to praise his players too much for the performance as he knows there is much work to be done for United to make it through to the semi-finals.
"We don't want a pat on the back for just getting a good performance," Moyes said.
"The job is to beat Bayern Munich. We want to beat them and knock them out."
Those are the kind of battling words that United fans long to hear.
For however much of a boost the result was, Moyes knows he and his players have let the club's loyal support down on the whole this season.
The worst disappointments have come in the league. Big reverses against Manchester City and Liverpool mean United now stand 10 points off the top four with six matches left.
If United fail to beat Newcastle on Saturday or Liverpool beat West Ham the day after, the Red Devils' hopes of retaining the Barclays Premier League will be mathematically impossible.
Some pride and momentum will therefore be gained if United can win at Newcastle, so Moyes wants his players to totally forget about Wednesday's second leg against Bayern until Saturday night.
"The only thing we are thinking about is the Newcastle game," Moyes said.
"The focus is all on Newcastle. We have to go up there, try to put on a good performance, pick three points up and keep trying to build up some momentum towards the end of the season."
Rio Ferdinand and Vidic started on Tuesday, but they could be replaced by Chris Smalling and Jonny Evans, who have been out for one and two months respectively.
"We have got Jonny Evans and Chris Smalling back in training, that helps us," Moyes added.
Ryan Giggs looks set to miss the trip to the north-east because of a hamstring injury he suffered against Bayern, but left-back Alex Buttner has recovered well from the hamstring problem he sustained versus the Germans.