Shepherdson underwent arthroscopic surgery on his right knee three weeks ago and is facing a race against time to be fit for the showpiece event in France.
The team fly out to Portugal on Thursday with the 25-year-old keen to show he is worthy of a place in the final squad.
"(Wallabies medical-coordinator) Dr Martin Raftery has decided to take the conservative approach and give me until Portugal until I need to run again," Shepherdson said.
"They're reasonably happy with how it's going I just think they don't want to risk it any more than they have to at the moment."
Shepherdson revealed he had been battling the injury prior to the Bledisloe Cup decider in Auckland four weeks ago and conceded the timing is less than ideal.
But he remains positive the injury will not deprive him of the chance to take part in his first World Cup campaign.
"I'm concerned that I'm not 100% going into a World Cup at the moment, but I mean that's just part of it and something you've got to deal with all year round playing rugby," Shepherdson added.
"I guess the fact that it's a World Cup makes it a little more concerning for me but the coaching staff and the medical staff are pretty confident so hopefully things can go to plan over the next few days and I'll be available for selection for that first game against Japan."
Australia captain Stirling Mortlock was another to miss afternoon training in Sydney on Monday as he has a stomach virus.