The London club returned to the foot of the Barclays Premier League on Saturday after they suffered their seventh defeat of a so-far winless season at Stoke. Speculation continues to mount over the future of Rangers boss Hughes despite public statements of support from Fernandes, who is also the club owner.
Marsh, who played over 200 games for QPR, told BBC Radio Five Live's Sportsweek programme: "I believe you should give the manager until Christmas. If you look at any successful team it is always based on continuity and consistency."
He added: "Just look at Arsenal and Manchester United and what they have done with Arsene Wenger and (Sir) Alex Ferguson.
"Yes, they have gone 11 games without a win, but I hate it when owners keep on sacking their managers after a run of bad results.
"Mark Hughes has been under the cosh for the last four games. It was only six games into the season when they were saying 'Hughes out'. That can't be good for anybody within the football club. I believe in continuity and consistency."
Although Marsh is confident Hughes can drag the club out of the bottom three, he believes Fernandes made a mistake in sacking his predecessor Neil Warnock.
"I wouldn't have sacked Neil Warnock in the first place," he said. "He got them to the Premier League. He was doing a decent job."
Fernandes took to Twitter on Saturday night to insist QPR are improving under Hughes, but he stopped short of giving his manager a full vote of confidence on the micro-blogging site, as has been the case in recent weeks.
The Malaysian also said next week's game against fellow strugglers Southampton was a "must-win" encounter, and Marsh agrees. "Both teams are having nightmare seasons," Marsh added. "They are in desperate trouble. It wouldn't be a stretch to say that the team who loses that match will get relegated."
Source: PA