The Ecuadorian winger has been in outstanding form since returning from injury, scoring a goal against Blackburn as the Red Devils increased their lead at the top of the league
The game seemed destined for a draw until the Ecuadorian winger hit a thunderous drive from the right hand side of the penalty area across the face of goal and into the far corner with 10 minutes left to go.
"Antonio could be very important," Sir Alex told reporters. "His form before he got the hamstring injury was outstanding.
"Now he' back we hope he stays fit because he's such an honest, hard-working player. He's got everything, really.
"You get two sides to Antonio. He's prepared to work really hard. He can tackle, he can run, but he can also beat a man.
"He's got exceptional talent and yet people underrate him. We don't, that's why we bought him and now he is back and in that form it gives us a big chance."
Valencia himself stated that he will continue striving to improve, and admitted he is very happy to be back playing following his injury.
"I try and strive for continuous improvement and I am always looking to improve from one game to the next," Valencia said.
"If it's a case of analysing stuff, it's really down to the manager and the backroom staff to give their opinions on that.
"It's just down to me to keep working hard and improving. It does make you happy when you hear positive things in the media and from the fans.
"All you can do is be grateful and thank people for that. I suppose it does encourage you to fight even harder to work towards that goal and that goal is obviously to win trophies.
"I'm very happy to be back and it's good to be playing now until the end of the season, hopefully.
"I get really pleased and full of emotion when I score. But to be totally truthful, I prefer playing the perfect pass for someone else to score. I like that, it's a good feeling.
"I think maybe I've got to leave it until I get to three or four goals and then smile more. What I really need to do is to learn some kind of dance routine or something!"