Soon after their match ended, Martin Klizan expressed sympathy for Novak Djokovic after he stunned the struggling Serbian star in the first-round round of the Barcelona Open.

"I want to wish him all the best," Klizan told Sky Sports. "I'm sure he will come back stronger."

Kind words. Nice sentiments. Many, including Rafael Nadal, have said similar things. Despite the well-wishes, this question is growing ever louder: "So just when will Djokovic come back even half as strong?"

"I feel I haven't lived up to your expectations, not even my own," the 30-year-old Serbian star admitted on Sky TV in Barcelona. "It's hard to deal with these types of games and defeats. I will try to continue and see where it takes me."

We are almost a full third of the way through 2018 and the 12-time Grand Slam singles champ Djokovic is 5-5, his worst start since his first year on tour. His confidence is obviously in tatters. His surgically repaired right elbow is no longer painful, but it remains an ongoing subject of conversation. And opponents he once rolled through -- Klizan being a perfect example -- are showing him that payback is a daily fact of life for slumping titans.

"Everybody he dominated over the years is walking on the court now with a different attitude," ESPN analyst Brad Gilbert told ESPN.com. "If you're Novak, whatever they say, the guys you smoked are not feeling badly for you because you're struggling. I'm not going to say [Djokovic] can't get it back -- look at Rafa and Fed. But Novak has to realize his situation."

Gilbert feels Djokovic isn't moving as well as he did in his glory days, guessing that he might have become too thin. Others say Djokovic waited too long to have surgery on his elbow, then jumped back into competition too soon.

The ongoing upheavals of Djokovic's coaching situation are certainly a baffling aspect of his recent history. His last official full-time mentor was Boris Becker, who guided him through his most prolific period but walked out late in 2016, citing Djokovic's flagging commitment.

When Becker left, Djokovic's personal, as well as professional, life were in flux. Once a finely tuned machine, Djokovic began spinning out in the turns once he went solo. He hasn't won a Grand Slam title since completing the career Grand Slam, at the 2016 French Open.

Andre Agassi stepped in last spring, as a pro bono friend and adviser. Radek Stepanek, a recently retired Czech pro, also joined the team later in the year. He was looking for a more formal arrangement that never materialized. Stepanek and Agassi were out by the end of the Miami Open. Agassi conceded he and Djokovic too often found themselves "agreeing to disagree." Stepanek just wasn't the right fit.

Still, Djokovic appears to be motivated. That could be partially a result of his recent reunion with Marian Vajda, an easy-going coach who guided Djokovic through the longest, calmest period of his pro career. They began working together again earlier in the month in Monte Carlo, though no long-term commitment has been made.

Novak Djokovic is off to a disappointing 5-5 start this season. Josep LAGOJOSEP LAGO/AFP/Getty Images

"Vajda knows me better than any tennis coach I've worked with," Djokovic said. "He's a friend. He's someone I can share a lot of things with, whether it's professional or private life. He's always there for me. He knows me inside out. He knows what I need in order to get to the highest possible level of play."

Anyone hoping that Vajda would provide a swift fairytale ending to Djokovic's struggles may end up disappointed, as the Klizan match suggested. Gilbert knows how laborious a process it can be to build confidence. He coached Agassi in the late 1990s, a period that included Agassi's terrible slump in 1997 as well as his subsequent return to pre-eminence.

"It was a process that took about 18 months," Gilbert said. "I'm not sure Novak is aware of how much it can take to come back or what you really need to do to recover. I'm not sure he ever talked with Andre about it. But maybe putting Vajda back in there is a good thing."

A top player needs three paramount things to function at or close to his peak: health, confidence and a solid support team. Djokovic admits it was probably a mistake to play Indian Wells and Miami so soon after his elbow surgery, but he said was pain-free in the long run-up to Monte Carlo.

He showed signs of life there, winning his first two encounters and was inspired to ask for a wild card into the tournament he hadn't played since 2006, Barcelona.

But that was a step in the wrong direction, even if Djokovic is feeling rejuvenated by teaming up with Vajda, who hopes to prove that he is indispensable as a coach.

Of course, that means Djokovic needs to start winning, and at this point, that's hardly a guarantee.