The 29-year-old has finally started to repay the £30.75-million United paid Tottenham Hotspur for his services two years ago, with six goals in seven Premier League games this season.
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"I just had a word with him at the start of the campaign," said Ferguson.
"I told him: 'Look, only you can solve this conundrum. You're the one in control here. You've got fantastic ability and you need to realise that ability and make the most of it. We'll be here to support you'.
"And he's started the season in terrific form for us. Dimitar has been, without doubt, our star forward."
"When you bring a player to Manchester United, not everybody takes to the situation straight away," he said. "Not all signings become hits overnight.
"[Antonio] Valencia did, of course, but he's almost an exception. Others take time, and Dimitar was a bit like that. It's just a fact.
"Nobody's ever doubted the ability of the lad, but what we're seeing now is a striker who's playing with belief and confidence."
Ferguson believes that the Bulgarian's blistering start to the season is down to two attributes that were missing from Berbatov's game last term.
"All strikers are massively reliant on those two factors - belief and confidence. And at the moment Berbatov has both."
