John McEnroe fears Novak Djokovic’s burgeoning spirituality could be draining the Serb of his “killer instinct”.

The American, who wrestled with his own volatile personality for much of his career, says of the one-time shirt-ripping beast of the Tour: “From an emotional standpoint he perhaps felt he wanted to bring in somebody who wants to give people a lot of hugs. That does not necessarily translate to having that killer instinct. It does not automatically lose it, but you don’t want to get into a situation where it is all peace and love and then have to go out and try to stomp on somebody’s head in competition.”

That is a not-so-oblique reference to the influence of Djokovic’s spiritual adviser, Pepe Imaz, the former Spanish fringe player he brought on board last year. Imaz has worked with him since 2013 and sits quietly in his box, a beatific figure of calm looking down on the drama of his friend’s increasingly erratic performances.

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Djokovic, if he wins, cups his hands from his heart towards the crowd, seeking a public embrace he plainly hopes is mutual. To some, it is an unalloyed gesture of love by a caring and sensitive man; to others, it is an embarrassing affectation.

Imaz, who runs a tennis academy in Spain for underprivileged children, called “Amor y Paz” (love and peace), told the Spanish sports paper Marca in May: “This type of work became known with Boris Becker leaving [last December]. A very important person. It is logical it draws attention. And so [people] jumped to the concept of hugs, love, and Pepe Imaz. It’s the same as before. He is having a moment he does not like, he would like to win more matches. And he’s working to do it.”

McEnroe observes: “I am imagining it is a work in progress. But it is a combination of things – whatever is going on off the court. He had an injury [a year ago], a let-down, and all this stuff contributes to it. I kept thinking it was going to get better.”

But it all went horribly wrong in the saddest meltdown of the summer, Djokovic, the defending champion at Roland Garros, giving up in the third set of a five-set match to the relentless young Austrian Dominic Thiem. He left the clay of Paris for the grass of London not like a contender but disillusioned and lost, with nobody at his side but Imaz, whose tennis expertise resided some way in the past.

Djokovic’s angst lingers as he awaits confirmation that his other new mentor, Andre Agassi, will be with him at Wimbledon next week. So anxious is the three-times champion about another assault on the title he is risking embarrassment in the high winds of Eastbourne to knock his tennis back into shape; Djokovic has not played on grass between the French Open and Wimbledon since 2010.

Agassi will not be at Eastbourne. If he comes to Wimbledon it is unlikely to be for the fortnight. He stayed for less than a week in Paris and he spent much of his time there promoting a brand of coffee and the tournament’s watch sponsor before leaving on the eve of Djokovic’s collapse against Thiem.

Djokovic was so dominant for so long that even this slight decline has people wondering if he is getting ready to quit. He and his wife, Jelena, are expecting a second child in August, yet the joy and self-assurance on court that he derived from the arrival of their first child seems to have evaporated.

The world No117 Denis Istomin put him out of the Australian Open in the second round. Nick Kyrgios beat him back to back on hardcourt in Mexico and California; Alexander Zverev blitzed him in Rome; Thiem destroyed him in Paris. The young gunslingers scent blood.

McEnroe, who will be as fascinated as everyone else watching the story unfold at Wimbledon from the BBC commentary box, says: “We will have to look at this in a couple of years. It is pretty quick to say: ‘Whoa!’ He’s 30, but we were talking about him blowing past Federer [in terms of grand slam wins] only at Wimbledon last year. Or at the very least Nadal. Nobody is sure what is wrong really.”

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If Djokovic decides to follow Federer’s example and take a short break from the Tour, McEnroe thinks it would happen after the US Open, where Djokovic would fancy his chances of winning.

Meanwhile, Djokovic waits and waits for Agassi, his Godot. Pat Cash said on Eurosport last week: “I’m not sure if Andre’s going to be turning up the whole two weeks or not but they’re certainly working towards a partnership in that way and I think it’s a good thing. “I mean, who wouldn’t want Andre Agassi in your corner?”

Whatever happens, Djokovic has already done wondrous things. As McEnroe says: “I think it’s safe to say that it’s tougher to stay there than get there. These guys have had phenomenal careers – Novak at 12 grand slams already. I suppose we shouldn’t be totally shocked after being the first guy in 47 years to hold all four slams that there would be a let-down.”

It is easy to think they are supermen, but they are all vulnerable.