The Springboks depart for France on Monday with coach Jake White still hopeful that centre de Villiers and winger Ndungane can overcome respective rib injuries.
Both players will undergo a fitness test on Friday before a decision on their World Cup participation is made.
"It's up to the medical team to make the call," said de Villiers, who has been spending time in a decompression chamber in an effort to speed up the healing process.
"They'll have to decide what is best for the team and what is best for me.
"I'm feeling good though and confident I'll be on the plane. I started running on Tuesday and didn't feel any discomfort.
"But I'll be fighting hard to be fit for the opener against Samoa (on September 9)."
White has already lost flanker Pierre Spies from his original 30-man selection due to a pulmonary embolism in his lungs.