But Djokovic enters 2019 as the man in form having won Wimbledon and the US Open last summer while Nadal is still recovering from an injury issue.
Federer has won the last two Australian Opens, but showed signs of slowing down in the latter stages of 2018.
And Croft suggests Djokovic has all the tools to replicate his Career Grand Slam achievement three years ago.
“Tennis can be unpredictable at times, but Djokovic appears to be ready to dominate once again,” Croft told Tennis365.
“It was only two years ago that I felt Andy Murray had finally broken the stranglehold of these amazing champions who have dominated the game in Roger Federer, Rafael Nadal and Novak Djokovic, when he became No 1 and ended that season on such a high.
“He looked like he was taking the game to another level, yet injury meant Murray has not been able to kick on from that fantastic achievement of rising to the top of the rankings and instead, we have seen the Big Three storming back and winning most of the big tournaments since then.
“As we go into 2019, it looks like Djokovic has separated himself from the pack a little once again, with his form at the back end of last year suggesting he will be the man to beat at the Australian Open and all the events he plays in this year.
“Yet the reason why we all love watching tennis is the unknown, the factor that has seen Murray fail to build on his rise to No 1 and the reason why Rafael Nadal has not been able to sustain his place at the top of the rankings despite appearing to move ahead of the chasing pack at times in his career.
“Novak looked unbeatable at times in the second half of last season, as he shook off his elbow problem and appeared to get back to playing his best tennis.
“Even his coach Marian Vajda has said he is playing better than he was when he was so dominant in 2015, so he is really laying down the marker for the rest.”