Marouane Fellaini
Marouane Fellaini has made 15 appearances this season.Getty

Manchester United midfielder Marouane Fellaini has applauded Louis van Gaal's surprising decision to deploy him as a second striker during the FA Cup replay 3-0 victory over Cambridge United.

After more than five months at Old Trafford, the Dutch boss keeps looking for the best formation to adapt to his players, having used both the 3-5-3 and the 4-4-2.

Some fans and pundits have questioned recent decisions like playing with three centre-backs, overlooking £26m summer signing Ander Herrera or deploying Angel Di Maria as a striker rather than on the flanks during the recent victory at QPR.

The boss made a new surprising decision against Cambridge by giving Fellaini a role as a second striker - ahead of Juan Mata and Wayne Rooney and just behind Robin van Persie – but this time his choice looked vindicated by the Belgium international's performance, who was involved in two of the three goals of the game.

After the game Van Gaal explained his decision as Cambridge "have very tall players."

"With Fellaini, we have always also an attacking point through the air. Cambridge have very tall players and we could score also in the air and not only along the floor. That was our game plan and he [Fellaini] confirmed that [his aerial prowess] again," van Gaal said.

After a maligned debut season at Old Trafford following his £27.5m move from Everton, Fellaini is starting to prove his worth under the Dutch manager, having also recently scored a goal in the victory over QPR thanks to his aerial prowess.

"It was okay [playing in attack]. The manager decided for me to play there. It was good for me. I played and we won so it's good for the confidence as well." Fellaini told the Manchester United official website.

"We created a lot of chances and we could have scored more goals. But 3-0 is good. It was a great chance for them [early on when Tom Elliott hit a post] but the most important thing, in the end, is we won the game and we are through to the next round."

With United now facing Preston North End in the fifth round, Fellaini hope to take advantage of the earlier eliminations of both Chelsea and Manchester City to win the title.

"In England, the FA Cup is a very big competition so it's good to be there [in the fifth round]. We have to stay focused for the next round and work hard together to get through again. It's difficult to play against these teams. It's the FA Cup so anyone can win a game. That's why you have to stay focused and be ready.

"When you don't concede a goal and you win, it's good for the confidence - for the players, for the club, for the supporters - so we have to keep going."