The Denver Post quoted Salt Lake City Police Det. Rick Wall as saying McGregor died of natural causes and police "didn't see anything suspicious."
McGregor was in Salt Lake City with Rockies chairman and CEO Charlie Monfort and executive vice president Greg Feasel, according to a team press release. When McGregor couldn't be reached Tuesday morning, the Post reported, an associate contacted hotel officials to check on him.
"Words cannot describe the level of shock and disbelief that we all are feeling this morning at the loss of Keli," Monfort said in a statement. "Our thoughts, our prayers are with Lori and the entire family as we all try to cope and understand how such a tragic loss could occur with such a wonderful man."
McGregor was named president of the Rockies on Oct. 18, 2001 but had been with the organization since October 1993.
The Iowa native was an All-America tight end at Colorado State and a fourth-round draft pick of the Broncos in 1985. He played in eight games that season -- two for Denver and six for Indianapolis -- and also spent time with the Seahawks. He was inducted into Colorado State's Hall of Fame in 1996.
He came to the Rockies from the University of Arkansas, where he spent four years as an associate athletic director. Prior to that he spent two years on the football coaching staff at the University of Florida.
McGregor is survived by his wife, Lori, and four children.