IRVING, Texas -- Dallas Cowboys starting fullback Tony Fiammetta still doesn't know what's wrong with him, but the symptoms he's endured the past two weeks have subsided and he anticipates playing soon -- perhaps Dec. 11 against the New York Giants.

Cowboys coach Jason Garrett on Wednesday ruled Fiammetta out for Sunday's game against the Arizona Cardinals. The Cowboys made a roster move earlier Wednesday, elevating rookie fullback Shaun Chapas from the practice squad to the 53-man roster.

Fiammetta has been tested for numerous ailments related to symptoms that include nausea and dizziness while working out.

"We're just trying to get to the bottom of it," Fiammetta said. "I'm starting to turn the corner and hopefully I'll be ready for next week."

Fiammetta became ill after the Oct. 13 win over the Buffalo Bills and has missed the last two games because of the undisclosed illness. He said the issue is not life-threatening but still strange because medical officials are unable to tell him what's wrong.

Yet his health is improving.

"In the past couple of days I made a bunch of strides," Fiammetta said. "It's just we have to see how it goes this week and hopefully the rest of the season this won't come up again."

Without him the last two games, the Cowboys averaged 85.6 yards and 3.2 yards per carry a game. With Fiammetta in the lineup, the Cowboys averaged 145.8 yards a game and 5.6 yards per carry.

Tight end John Phillips took over for Fiammetta at fullback and played nearly 50 snaps as the lead blocker for running backs DeMarco Murray and Felix Jones.

"I want to see the team succeed whether I'm there or not," said Fiammetta, who started attending meetings and working out lightly at Valley Ranch this week. "And hopefully when I come back, I can continue to do what I was doing before and help the team win some games."

Fiammetta's vegan diet, which eliminates the use of animal products, has been ruled out as a possible cause of his symptoms. Fiammetta said if anything, that diet has helped him, although he does miss having steak.

"I wouldn't be doing it if I didn't think it was good for my health," he said. "There are people who are concerned about that. I wouldn't worry about that."

Calvin Watkins covers the Cowboys for ESPNDallas.com.