The 28-year-old was handed a second yellow card for diving during Chelsea's 3-2 defeat to the Red Devils, despite replays showing that defender Jonny Evans did scrape the forward's shin.
"Well, did he intend to dive?" said Ferguson. "Jonny may have just caught him a little bit but you can either carry on running, which he could have done, but he chose to go down. He could have carried on and scored. That's what I can't understand."
Chelsea defender Branislav Ivanovic was also shown red during the clash at Stamford Bridge yesterday.