The United captain was benched against Stoke City before returning to the starting line-up for the 0-0 draw against Chelsea on Monday.
Rooney's display impressed former team-mate Ferdinand, who believes the 30-year-old England international could turn United's season around.
"Wayne will have been hurt and desperate to prove a point," Ferdinand wrote in a column for The Sun.
"He didn't score and was lucky not to be sent off for a nasty tackle on Oscar. But other than that, his all-round game was superb.
"So, one of two things must have happened.
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"Van Gaal may have taken the shackles off and allowed Rooney to go out and express himself.
"Either that or Wayne has thought, 'Sod it, I’ll play how I want to play'. Whatever it was, it worked."
Ferdinand said he saw a change in United thanks to Rooney's impact, despite Van Gaal's men seeing their winless run stretch to eight games.
The 37-year-old, a six-time Premier League winner with the club, said Rooney provided a much-needed option for United in attack.
"Rooney played with freedom against Chelsea and you could see how the team grew in confidence as a result," Ferdinand wrote.
"He was coming off the centre-back to help link the play or spin round and mount an attack. Then he was drifting out to collect and hit those fantastic diagonal balls and, most importantly, he was getting in the box as well.
"Every time United had the ball, Rooney was finding space to make himself available.
"And, crucially, his team-mates were giving it to him with a forward pass hit at pace."