The Whites currently sit bottom of the Barclays Premier League and have not won a league fixture since a 2-1 victory over West Ham on New Year's Day.
Meulensteen was appointed as Martin Jol's successor in December but, having been unable to steer Fulham out of the relegation zone, he also lost the faith of owner Shahid Khan.
Brevett, who currently manages Southern League Premier Division side Arlesey Town, reckons the players will struggle to once again adapt to new ideas.
"The players will be shocked," he told Press Association Sport.
"Some are players that Meulensteen brought in in January and they just won't know what has happened.
"As players you have got to get on with it, it is your job and you have got to get on with it. They have to take responsibility but it is true, you do also need continuity in what you're being told is expected of you.
"Just as they are getting used to Meulensteen's methods and the things that he wants, he is gone and another manager comes in - it will be very difficult for him with 12 games to go, it doesn't happen over night."
Magath, who has won three Bundesliga titles during his managerial career, now has 12 games to turn things around at Craven Cottage after becoming Fulham's third manager of the season.
Brevett feels a relegation battle requires a different approach and also did not rule out Khan making another change in the summer if Magath fails to keep the club in the top flight.
"He owns the club and will do what he thinks is best," added Brevett.
"He has brought a new manager in with 12 games to go, if Magath doesn't keep them up is he going to bring in another manager to get them out of the Championship? How much does Magath know about that division?
"Sometimes when a new manager comes in you get a new kick and hopefully if they do that they might have a chance.
"The confidence is low and it is going to take a completely different mindset, there are a lot of differences between fighting to win things and trying to stay in the league. We will have to wait and see what he comes up with.
"Fulham have flirted with relegation a few times but nothing as serious as we see now, it is massive. Financially and for the fans as well.
"It means everything to stay in the Premier League. They will be doing their upmost to stay there."
Fulham Supporters' Trust member Dan Crawford said fans were also 'surprised' by the decision to sack Meulensteen, although results may have justified the change.
"I was very surprised," he said.
"We had all read that he might have two games to save his job but you just assumed that the performances and fight they showed would have been enough.
"We haven't won a league game since January 1, we are out of FA Cup, bottom of the league and running out of time.
"The defending has been abysmal for most of the season, you hope that someone who is a disciplinarian will come in and get things right, he won't take any prisoners and has virtually no margin for error.
"We are in the last chance saloon and everyone recognises that, it slaps a little bit of desperation but that is par for the course given the situation we are in."
Magath will not face the media until he hosts a press conference previewing next Saturday's crucial Premier League clash with fellow strugglers West Brom.
A win in the German's first game would see Fulham close the gap on the 17th-placed Baggies but a defeat could see them cast further adrift with time running out to continue their 13-year stay in the top flight.