Dennis took to the start of stage 1 but began suffering with what the team described as 'flu like symptoms' in the latter stages, eventually finishing over six minutes behind the day's winner Nacer Bouhanni (Cofidis).
The Volta a Catalunya was set to be Dennis' first race in Europe after he was forced to miss Paris-Nice after falling ill with sinusitis a few days before.
"I was feeling good when I arrived in Catalunya on Sunday. It looked like I was 100% but obviously there was something underlying and racing yesterday has flared it up. It's disappointing not to continue racing here, but I have some big goals for this year, which are still to come and my health comes first," said Dennis.
With Richie Porte and Tejay van Garderen leading the team, the pressure was off Dennis in Catalunya as he looked to bounce back from the illness that had kept him out of Paris-Nice. Team doctor, Dr Daniele Zaccaria said that decision to remove Dennis from the race was so as not to harm the Australian's health any further.
"He was dropped in the final 10 kilometers which is unusual for him on such a course and this was an indication of his condition," Dr Zaccaria said. "He has a fever and didn't sleep well last night, so it is in his best interests not to start today in order to avoid any further illness and jeopardize his long term plan for this year."
Dennis' programme has not been defined and the team did not make any indication as to when he might make his comeback.