Bernard Tomic cited an off-season focus on fitness work as the primary reason for his first-round loss to David Ferrer at the Brisbane International on Monday.
World number 26 Tomic delivered an error-strewn and lethargic display in his maiden outing of 2017, going down 6-3 7-5 to Ferrer, the eighth seed.
After his defeat, the Australian highlighted his time away from the court in recent weeks.
"I'm never going to be the fittest guy but I can do so much more," said Tomic. "But I feel like that workload, doing different things for the past month, having so much time off tennis, it was tough to react and come into this match.
"There's a huge possibility that doing a lot of fitness and having so much time away from tennis had a lot to do with this match."
Seventh seed Grigor Dimitrov breezed past Steve Johnson 6-2 6-3, while there were also first-round wins for Kyle Edmund and Nicolas Mahut. Viktor Troicki was a set up on Yoshihito Nishioka when play was suspended due to inclement weather.
Rafael Nadal headlines Tuesday's schedule in Brisbane, the Spaniard facing Alexandr Dolgopolov as he continues his preparation for the Australian Open.
This is the first time Nadal has opted to compete in Australia in the opening week of a season and crowds gathered to watch the Spaniard practice on Monday.
"It's true that Doha worked well for me in the past [as a first tournament of the year], but here in Brisbane is something that probably will help me to adapt quicker to the Australian conditions that are always a little bit tougher in terms of weather," said Nadal, who returned from injury with victory at last week's Mubadala World Tennis Championship.