The Mexican netted twice to help the Red Devils seal a 3-2 Champions League win on Tuesday evening, despite having trailed 2-0 in the first half.
And, after the game, Sir Alex conceded that he faces a selection headache with Robin van Persie, Wayne Rooney, Danny Welbeck and now Chicharito all amongst the goals recently.
He told ITV: “[Chicharito] is improving all the same and he’s got such enthusiasm for the game. He trains magnificently.
“He’s got me thinking, I must say that. He’s got me thinking about him and Van Persie, Rooney and Welbeck.
“I don’t know what to do with them, to be honest with you.”
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The Scot also defended his decision to start Michael Carrick and Alexander Buttner in defence ahead of Rio Ferdinand and Patrice Evra, insisting a congested fixture list makes rotation a must.
He added: “I think we did the right thing. It wasn’t Michael Carrick’s fault for the goal – the first goal – he did his job well.
“He can take the ball out from the back for us, his passing was terrific.
“I think you have to look at the big picture. Rio, at his age, big game on Sunday against Chelsea, then Chelsea on Wednesday and Arsenal on the Saturday... we’ve a massive problem coming up now and it’s important to use and utilise the squad that we have.
“OK, at the moment, with Vidic out and Jones and Smalling not available, putting Michael at the back there is not the best but he does the job well.”
The Red Devils manager also praised his side’s recovery from two goals down but expressed his concern at their defensive shortcomings.
He said: “It’s been the story of our season at home, starting badly and losing goals. We’re having to fight back to rescue games and it’s the front players who are doing that for us.
“I must say, some of our football was terrific tonight – some fantastic football, we created a lot of chances – but it is a concern, losing the goals.”