Sir Alex's revelation in May that Rooney had handed in a transfer request sparked a summer-long saga in which the 27-year-old pushed for a move to Chelsea.
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Rooney netted twice in United's Champions League group-stage victory over Bayer Leverkusen on Tuesday and Sir Alex believes the forward has recaptured the form of his best years at Old Trafford.
"I thought Wayne was fantastic [on Tuesday]. He's got his energy back, his determination, his purpose to attack," Ferguson told MUTV.
"Being a director, I'm delighted to see that. He's back to what we always remember."