The Scotland international has been in sparking form for the Bhoys in the last few months.
Griffiths scored 9 goals in his last 8 league games for the Premiership champions, and the reasons why were apparent when the former Wolves man joined up with the Scotland squad for international duty.
“Some of our medical team commented that they felt he looks better," Gordon Strachan's assistant told STV. "He looks leaner, looks a better body shape than he did maybe some of the other times he’s been with us.
“So clearly there’s been an improvement in Leigh in lots of ways. You could argue what comes first. I would imagine the physical change probably has resulted in him doing better in terms of his productivity. I think he looks a better player.”
Griffiths was Celtic's top scorer this season with 20 goals, and the Scottish Premiership's second highest scorer after Adam Rooney with an impressive 14 strikes in 24 games.
It capped a strong season for the former Wolves striker, who has rediscovered the sort of form that convinced Celtic to sign him in 2013.
The 24-year-old managed 7 goals last season in the 14 games he played, having scored 13 times for Wolves in the first half of that campaign.
McGhee was himself a former striker at the Bhoys in his playing career, helping Celtic to two league titles during a four-year spell in Glasgow in the 1980s.
And so it's no surprise to see the 58-year-old so happy with another Bhoys frontman hitting a purple patch, and McGhee added that he has noticed Griffiths moving more intelligently in the box in Celtic matches.
"I think since Christmas he’s done brilliantly," McGhee added.
"I was speaking to him this morning about what he’s done since then - what was said to him in terms of his coaches, about playing that role up front by himself, about getting across the front post.
"Clearly from what he said that’s the things that they've put right with him. They’re getting him across the front post and getting him in to the epicentre of the action, where the ball is likely to land.
"Rather than pulling away and looking for secondary balls, rebounds and stuff like that. He’s trying to get the first one and I think that’s made a difference to him."