The ex-Everton boss took over from Ferguson in the summer following the 71-year-old's decision to retire from the game after 27 years leading the North-West outfit.
Despite Ferguson's exit as manager, the Scotsman remains a director at the club, which Bosnich believes could affect Moyes in a negative way.
"I remember the late Sir Matt Busby when he stayed on in a director of football role and there was talk of him perhaps having his shadow over the following managers Wilf McGuinness and Frank O'Farrell," Bosnich told talkSPORT.
"It didn't maybe do them the best to have him there. A lot of people said, 'well, you have got one of the best in the business as a sounding board,' but that can be double-edged. You are always in that man's shadow."
United have taken 11 points from eight games in the Premier League this season.