The no-nonsense midfielder heads into Sunday's Premier League clash at Burnley having already made more appearances for the club this season, 41 in all competitions, than in any campaign since his £27.5 million from Everton in 2013.
The Belgium international scored in last month's win at Middlesbrough, captained the team for the first time in the victory at Sunderland and on Thursday night came off the bench to help United book their place in the semi-finals of the Europa League.
Having often bore the brunt of criticism from a frustrated Old Trafford faithful during the tenures of David Moyes and Louis van Gaal, Fellaini has become a more reliable, and influential presence, under Jose Mourinho.
The 29-year-old said on the United website: " I feel like I have been playing well in the last few games.
"When the manager puts me in the team, I give absolutely everything for the cause. I have confidence in the manager and the staff.
"I'm confident, I know what I can do, so I feel good in my mind and my body. I keep going and keep working hard and, when I get a chance to play, I always try to do well."
Fellaini's form is a welcome boost for Mourinho, who has seen his side decimated by injury, particularly in defence.
Already without long-term absentees Phil Jones and Chris Smalling, the Portuguese lost Marcos Rojo in the extra-time win over Anderlecht.
The Argentinian left the pitch on a stretcher after sustaining a knee injury, while to make matters worse Zlatan Ibrahimovic reportedly suffered cruciate ligament damage that will rule him out until 2018 when his knee buckled in an awkward landing against the Belgians.
Read the full article on eurosport.co.uk: Manchester United midfielder Marouane Fellaini happy with his form