Alexander Zverev and Novak Djokovic
Despite his loss in the ATP Finals, Novak Djokovic will be a big favorite in 2019. In this picture, Alexander Zverev and Djokovic pose with their trophies following the singles final during Day Eight of the Nitto ATP Finals at the O2 Arena in London, Nov. 18, 2018. Clive Brunskill/Getty Images

Novak Djokovic can be considered the favorite for all four Grand Slams next tennis season, according to Andy Murray's ex-coach Greg Rusedski.

Although he most recently lost in the ATP Finals to Alexander Zverev on Sunday in what would have been a fitting way to end his 2018 season, it has still been a monumental year for the Serbian who ends it with two Grand Slams and an overall total of four titles.

He will now enter the 2019 season as the world No. 1 and having lost just three times in his last 38 matches, Rusedski believes he would be hard to stop next year, even on Rafael Nadal's preferred clay courts.

“I think it’s a fair statement to suggest Novak is favorite for all four Grand Slams next year,” Rusedski told Tennis365 before the ATP Finals. “The other players will be starting their pre-season programs now and they need to do something special to get near Djokovic because he is playing tennis that none of them can touch."

“He has separated himself from the pack and while Rafael Nadal is the one who will feel he can stop him when he gets onto the clay courts at the French Open, it is hard to see Novak getting beaten if he continues to play as he has been in the second half of this season."

In fact, Rusedski even made a bold prediction that given the way Djokovic had played over the course of the second half of 2018, he could eventually surpass both Nadal and Roger Federer's Grand Slam tallies.

Djokovic is currently on 14 while Nadal and Federer boast 17 and 20 respectively.

“The aura is back for Djokovic,” Rusedski explained. "It feels like the period when he had all four majors [in 2016] and the rest of the tour look at him and question how he can be beaten. He has set the bar so high. You look at the serve that has been so good this week, the ground shots are so accurate and you struggle to find holes in his game."

“I feel 2019 will be very important for him. If we wins the calendar Grand Slam, he will be up to 18 majors and while I would probably expect him to win three of the four, there is every chance for him to get to Federer’s 20 Grand Slams and go well past that. If he continues to play as he is right now, it is hard to see anyone stopping him."

The 31-year-old Djokovic is already a +150 favorite to win the 2019 Australian Open with Nadal just behind at +550 according to OddsChecker.

However, tennis has a way of being unpredictable and Rusedski acknowledged that anything could happen next year.

“That said, strange things can happen in this sport. When we saw Novak winning the French Open and completing the Grand Slam set in 2016, we all felt he was on his way to complete domination, but it didn’t quite happen for him after that," he added. “He didn’t win anything again until Wimbledon this year. So even though it’s easy to make predictions, things change and that is why we love watching this sport to see what might happen next.”