The already intense scrutiny at Old Trafford ratcheted up a notch this week when United bowed out of the Champions League at the group-stage juncture.
Compounding the ignominy of leading United in the Europa League is the criticism Van Gaal has faced from his own supporters for a string of uninspiring displays.
Van Gaal's side were held to their sixth goalless draw of the season by West Ham at the weekend, but Fellaini says he retains the full backing of the United squad.
"We trust him," the Belgium international told NBC Sports.
"He is the manager, it is his philosophy and we have to continue like that.
"I am sure the goals will come and the chances as well."
Furthermore, Fellaini believes United can win this season's Premier League under Van Gaal.
"Yes, of course (we can win the title)," he said.
"At the moment we are in the top four, we are there
It is a tough month but we have to continue like this.
"We know as Manchester United the expectation from us is high.
"Now we are focused, we know what we are doing
So, we will see but we are there."
Source : PA
Source: PA