Todd Palin is in serious but stable condition at a local hospital in Anchorage, Alaska, where he is scheduled to undergo surgery, according to the Iron Dog, the organizers of a 2000-mile snowmobile race Todd competes in every year.
An Alaska source tells PEOPLE Todd suffered "a variety of internal injuries" that include, according to another source in the Palin camp, two collapsed lungs. This source says Todd, 51 and in excellent health, is expected to pull through.
Kevin Kastner, executive director of the Iron Dog, tells PEOPLE that he's learned from Todd's father and others close to the situation that, "In general, Todd's got some serious injuries but it doesn't appear to be life-threatening at the moment. There are just some things they need to work on and they won't have an answer until probably tomorrow for a further assessment of what's going on. He was obviously hurt badly; they were able to bring him in and he's stable."
Kastner doesn't know where or when the accident took place but says he believes it was at the end of a recreational ride. "He was out with family and brought some of the family back and was headed somewhere else."
Sarah and Todd's daughter Bristol took her baby daughter, Sailor Grace, to visit her grandfather at his cabin in Alaska over the weekend. "Sailor's first time at Papa's cabin!!" Bristol captioned an Instagram photo of Todd holding Sailor and his son Trig.
Bristol posted another photo of her dad on Monday after news broke of his accident. "Toughest guy I know, thank you for all the love and support," she wrote.
Kastner tells PEOPLE Todd "is a fierce competitor" who's passionate about snowmobiling. "It is one of those things in his life that is truly Alaskan. It keeps him grounded and rooted and is kind of who he is as a person. There is this camaraderie that goes along with it. For him it keeps him grounded; it's the roots of who he is as an Alaskan and that's what brings him back."
Kastner says Todd's competitive nature is another thing that draws him to the Iron Dog event – the longest snowmobile race in the world – which he's won four times.
"That's a pretty strong record," Kastner adds. "It's part of who he is … He has the tenacity it takes [to win]. It's a physical and mental and mechanical event. It requires a broad spectrum of capabilities."
Sarah, the former governor of Alaska, was in Florida campaigning for GOP front-runner Donald Trump when her husband was injured. She abruptly canceled a Trump rally in The Villages, Florida, on Monday but stopped by another campaign in event in Tampa on her way to the airport.
"Thank you guys, for your prayers for my husband, who is recovering right now in the ICU after a little wreck on a snow machine," Palin told the crowd, "so thank you ... a big wreck."
Reporting by DIANE HERBST