Rooney scored twice in the 4-0 win against AC Milan on Wednesday, taking his tally to 30 goals this season.
Cristiano Ronaldo scored a record 42 goals in the 2007-08 season for United.
Ferguson said: “It’s a challenge [for Rooney to get 42 goals]. I was just happy for him to reach 30, to be honest with you.
“But he keeps on improving and he was sensational again tonight.
“He is still carrying an injury, nothing serious, but with a game on Sunday (against Fulham) we wanted him off early.
“His performance was a continuation of his form over the last two or three months, just sensational, unbelievable. I’m very pleased with him.
“What’s improved is his movement in the penalty box. He’s also practiced a lot more than he has ever done.
“After training, he puts extra work in and that’s what we’re seeing now – he’s reaping the rewards of that.”
He said: “We beat Milan 4-0 and not many teams have done that. I don’t know if anyone has done that.
“The deciding factor was Rooney’s goal just after half time. That finished the tie.
“We were able to relax, play good football and keep our concentration after that.
“Milan had to force it and that made it difficult for them.”
