The midfielder played in the 2-0 victory over Man City last weekend despite carrying an ankle injury, and the centre-back believes this shows his professionalism
Fellaini has constantly been linked with a move away from Merseyside this season after a string of impressive performances have seen him top the club's goalscoring charts with a return of 11 goals from midfield.
However, Jagielka believes there are no doubts over the Belgium international's commitment to the club after he played a full 90 minutes of football despite carrying an ankle injury.
"He had a painful ankle problem before the City game and he could have milked it and missed the game before disappearing off on international week, but he was desperate to play," said Jagielka.
"He strapped himself up and put in a great performance. You cannot question his commitment.”
The England international, who himself missed last weekend’s clash with an ankle problem, also praised the 25-year-old's desire on the pitch.
Jagielka hailed the all-action performances that have seen him develop into a force at both ends of the field, and believes he is now playing at a level far more mature than his years suggest.
He continued: "Felli has taken all the beatings for us throughout the season and he will feel sometimes like the world is against him. Sometimes it has been.
"You can forget he is not that old. He hasn't grown up in the Premier League for all his career and hasn't been at this level as long as others."