"I'm 100 percent confident when I get here in February I'll be fine to drive and race and be able to do everything I need to do," Stewart told reporters at Florida's Daytona International Speedway.
Teams were scheduled to hold the first of two days of testing at Daytona on Thursday but the session was delayed by rain. The Daytona 500 is the season opener for NASCAR's Sprint Cup Series.
Veteran Mark Martin is testing Stewart's No. 14 Chevrolet this week while Stewart continues to recover.
Stewart, 42, is a three-time series champion and one of the sport's most popular figures, although he's never won the Daytona 500. He also is a co-owner of the Stewart-Haas Racing team, whose other three drivers are Kevin Harvick, Kurt Busch and Danica Patrick.
Stewart broke his leg while driving in a non-NASCAR sprint-car race in Oskaloosa, Iowa. After three surgeries, he's been undergoing therapy and now "I feel pretty good," Stewart said Thursday, according to a NASCAR transcript of the news conference.
"I still have a little ways to go, but we've got four weeks to get ready the rest of the way," he said.
But Daytona is a high-banked, 2.5-mile speedway where the drivers race flat-out with little braking, and Stewart acknowledged that "the hard part with here is ... with your right leg you're on the gas so long."
"That's the only thing we're worried about right now, just because you don't know until we get in a car and actually run," he said.