The 24-year-old has scored 15 goals in 33 appearances for his new club already this season, and Ferguson has been impressed by the former West Ham United's displays.
"The goal he got in Lyon was obviously really important to us, as were his goals at Liverpool, Tottenham and at home to Chelsea right on half-time when we were searching for that first goal," said the veteran United boss.
"He's proving to be an important player for us, no question. He's now on 15 goals. I think that's a great return in his first season with us so we're delighted with him."