Tony Stewart has pulled out of this weekend's Cheez-It 355 NASCAR Sprint Cup Series event at Watkins Glen International, after being involved in a regional racing accident on Saturday evening that resulted in another driver being fatally injured.

Stewart-Haas Racing vice president of competition Greg Zipadelli made the announcement on Sunday morning, just hours after indicating that it was "business as usual" for the team despite the tragic events at a sprint car short track event at Canandaigua Motorsports Park in which Stewart's car struck a competitor who had walked down onto the race track to remonstrate with Stewart over an earlier incident.

20-year-old Kevin Ward Jr. was immediately attended by medics at the scene and transferred to a local hospital, but was reported dead on arrival. [See separate story.]

"There aren't words to describe the sadness I feel about the accident that took the life of Kevin Ward Jr.," said Stewart in a statement released by the team. "It's a very emotional time for all involved, and it is the reason I've decided not to participate in today's race at Watkins Glen. My thoughts and prayers are with his family, friends and everyone affected by this tragedy."

"We know it's just an unbelievable tragedy," Zipadelli said at a press conference on Sunday morning as he informed reporters that it had been Stewart's personal decision not to race today at Watkins Glen so soon after the tragic events.

"Our hearts go out to Kevin and his family. Thoughts and prayers. This is a very tough, very emotional time for everybody - his family, our family at Stewart-Haas, Tony Stewart.

"We gave Tony some time to sleep on it and met with him this morning and he feels strongly that this is the right thing to do. We at SHR support it and agree with it. It's a difficult time for both parties. This is what we feel is right and we're supporting Tony in it," Zipadelli said.

"There's not a lot you can do. The only thing we can do is do what we feel is right. This is what we feel is right and are supporting Tony in it," Zipadelli added. "I support Tony Stewart, I think I have shown that over the last 18 years.

"He's way more than a boss. He's going through a tough time. It's emotional for him."

Nationwide Series driver Regan Smith will take over the seat of the SHR #14 for today's race. Stewart had qualified in 13th place for the event, but the change of driver means that Smith will now be starting from the back of the field alongside Stewart's team mate Danica Patrick.

Coming into this weekend, Stewart had held high hopes this would prove his best opportunity for making the Chase with a race win. Stewart has won at the Glen on five previous occasions, most recently in 2009.

Even though he won't start today's race or earn any championship points, Stewart still remains eligible for the Chase if he is able to claim a race win in one of the four remaining events at Michigan, Bristol, Atlanta and Richmond before the Chase cut-off. Stewart is currently only 19th in the points standings and highly unlikely to make the championship play-offs that way without a 2014 race win.

"Honestly, that is the furthest thing from our minds right now," insisted Zipadelli. "We're thinking of Kevin's family and Tony and the people at our company. That's something that, when we get home on Monday, we'll have to look at and evaluate and go through that and make decisions.

"Today is all about doing what we can today to get through today and get through it the best we can as a group, and try to do it in the right way. We haven't even crossed that bridge yet."

Saturday night's fatal accident is now under investigation by local authorities, with Ontario County Sheriff Philip Povero quick to point out that it is not being treated as a criminal matter at this time.

"This is right now being investigated as an on-track crash and I don't want to infer that there are criminal charges pending," said Povero. "When the investigation is completed, we will sit down with the district attorney and review it. But I want to make it very clear: there are no criminal charges pending at this time.

"[Stewart] was visibly shaken by this accident," added Povero. "People that witnessed it were horrified ... They were extremely shocked."

NASCAR earlier said that they had learned nothing about the incident that had inclined them toward asking Stewart to sit out Sunday's Cup race if he had wanted to compete.

"Everything that's been made available to us at this time would not preclude him from participating in this event here today," said NASCAR spokesman Kerry Tharp. "While it was a non-NASCAR sanctioned event, everyone in the motor sports community has feelings for these types of situations. We've been through them before.

"Our thoughts and prayers go out to the family, friends, and fellow competitors of Kevin Ward Jr." Tharp added in a subsequent statement. "We support Tony Stewart's decision to miss today's race and we will continue to respect the process and timeline of the local authorities and will continue to monitor this situation moving forward."