(CNN) - It appears as if Novak Djokovic faces a long and hard road back to his glory days on the tennis tour.
The Serb was once the most dominant player around -- winning four straight grand slam titles from 2015 to 2016 -- but little of that scintillating form was on display when the 12-time grand slam winner was upset by Japanese qualifier Taro Daniel 7-6 (7-3) 4-6 6-1 in the second round in Indian Wells on Sunday.
No wonder the injury hit Djokovic uttered to reporters afterward: "For me it felt like (the) first match I ever played on the tour. Very weird."
Djokovic -- who benefited from a bye in the first round -- relinquished a 5-2 lead in the first set and wound up committing 61 unforced errors.
Having enjoyed so much success in the California desert by winning five titles, Sunday marked his earliest Indian Wells exit since his debut in 2006. And he hadn't lost to any qualifier since 2008 in Miami.
As his form began to dip at the end of 2016, Djokovic admitted that he had been affected by off-court issues that he hasn't elaborated on. But his elbow problems certainly appear to be the much bigger concern.
Djokovic shut down his season after Wimbledon in 2017 and despite not being at his best, decided to play at this year's Australian Open where he was ousted by South Korea's Hyeon Chung in the fourth round.
He then announced in early February that he had undergone a "small medical intervention" on the elbow, before practicing in Las Vegas with his renown coach Andre Agassi.
Quick turnaround from surgery
"I was not even supposed to be here because of the surgery that was only five, six weeks ago," said Djokovic.
If the surgery wasn't enough, Djokovic looked like he had been suffering from illness on the eve of Indian Wells.
"I just completely lost rhythm, everything," said Djokovic. "Just struggled also a little bit with the health the last couple of weeks.
"But ... I was grateful to be out on the court after surgery that quickly. But at the same time, just didn't feel good at all.
"I made so many unforced errors that it was just one of those days where you're not able to find the rhythm from the baseline, especially from the backhand side. That has always been a rock-solid shot for me throughout my career.
"Just some inexplicable, uncharacteristic errors. But that's, I guess, it's all part of those particular circumstances that I'm in at the moment."
Del Potro backing
If anyone knows what it is like to deal with injuries, it's Juan Martin del Potro -- the career of the 2009 US Open winner has been ravaged by wrist injuries. But the Argentine backed Djokovic to recover.
"I think it's only (a matter of) time to get where he deserves to be," said Del Potro. "And if his body feels good, the tennis comes along and the confidence comes along too.
"But it's not easy to deal with this kind of frustrations after injuries or when you always be the favorite to win a tournament, you come here and you lose in first round.
"But he's strong enough to deal with that, and I love him and I want to see him in the top positions very soon."
For now, Del Potro -- given his strong start to 2018 -- would appear to be Roger Federer's major rival in Indian Wells.
While Federer completed a rain affected win over Argentine Federico Delbonis 6-3 7-6 (8-6) in his opener, Del Potro began his tournament by thumping promising Australian Alex de Minaur 6-2 6-1.
As for Djokovic, the question now is whether he will play in Miami later this month.