The 29-year-old on Saturday fights for the fourth time to become a world champion, against Russia's Fedor Chudinov at Bramall Lane for the WBA super-middleweight title.
He does so for the first time working since with McGuigan, having won each of his four fights since appointing him, and believing that after losses to Carl Froch and another by Badou Jack he will finally succeed.
After the Jack fight McGuigan succeeded Paddy Fitzpatrick as his trainer, and at a time when he had never overseen a defeat.
Conrad Cummings' loss to Ronny Mittag in November then became the first ever by a professional fighter he has trained. Since then he has also been criticised for Carl Frampton's tactics in his January defeat by Leo Santa Cruz, and for allowing David Haye to fight on with a ruptured Achilles in defeat by Tony Bellew.
On the same evening as Cummings' loss, Groves outpointed Eduard Gutknecht, who afterwards collapsed and has been left disabled when it appeared he could have been withdrawn.
His observation of each led to an introspection he believes he has overcome, but Groves said: "I thought to myself, 'Do I really know about Shane yet?'.
"I've worked with other trainers who get pushed up on a pedestal, then fall, implode and recover from it: have a breakdown.
"I was thinking, 'I hope this chap doesn't lose the plot'. He hasn't. He coped very well with the losses.
"More so with Frampton losing; Haye lost because he was injured. He would probably have won if he wasn't injured.
"He had David Haye in a fight, with one leg, for five rounds, and there'd be some people saying, 'You've got to pull him out'. But he's got to make a decision there and then.
"I remember thinking, 'I'd have left David in there', because he was doing all right. He's at a stage of his career where if he bails out with an injury, that's it, he's out. He's in with Bellew, who couldn't knock him out.
"If he was in there with (Wladimir) Klitschko or Anthony Joshua, would you have let him do another round? Probably not, no. But it's just hard to tell in the there and now, so you let time do its thing and then assess things."
Groves has spoken of the way the tragedy surrounding Gutknecht has affected both he and his wife, Sophie. His son, Teddy, is also nearly a year old.
But despite the harsh reality of the Gutknecht episode, his wife remains supportive of his desire to fight on.
"She's happy for me to carry on," he said. "She says it's okay as long as I am fighting for the right reasons.
"I'm still in boxing for the right reasons and I still have her total support. She has been around boxing long enough to understand.
"She knows that if I ever needed help, Shane would be there for me.
"I've had four fights with him, I've got enough proof that he's the right man; he's had I don't know how many world title fights where he's worked the corner."
