The Ecuador wide-man endured a slow start to life at Old Trafford following his £17million move from Wigan but is now making a major impact scoring three goals in the last six games for United.
"It is good to see him scoring," said Ferguson. "He did not show a scoring ability when he was at Wigan but when he came to us we talked about this and the fact if he is to progress his career, it was something he should work on."
The advice has proved to be accurate, with Ferguson delighted United seem to have unearthed another supply of goals as they look to cover Cristiano Ronaldo's exceptional return.
"He is showing evidence of progress now," said the United boss. "He has settled in and is emerging as a top performer.
"He has strength, good balance, speed and is a good crosser of the ball.
"But the main thing is that he is now playing with much more confidence.
"I am delighted with his steady improvement and hopefully he will prove to be another valuable source of goals as we move through the season."