The American, who is due to compete in the giant slalom on Thursday, will be supported closely by the Stifel US Alpine Ski Team coaches for the remainder of the season and in the future.
"After working with Mike Day for seven seasons, I've decided to move forward with new leadership on my team for the next phase of my career," Shiffrin said in a statement.
"I want to thank Mike and acknowledge all of his work and dedication over the last several years."
In 2016, Day returned to the US Ski Team to serve as women's head coach, working specifically with Shiffrin, after having served as a coach in various capacities for more than 15 years.
Day had previously coached Ted Ligety, who became a world champion and won two World Cup giant slalom titles during his tenure with the men's technical team from 2010 to 2013.
During Day's tenure with the US Ski Team, Shiffrin earned 65 of her World Cup victories, two of her three Olympic medals and 10 of her 12 world championships medals.
Shiffrin is in the midst of a record-breaking season having broken the women's record of 82 World Cup wins she shared with compatriot Lindsey Vonn (38) in January.
Shiffrin is now one win away from equalling Swedish men's slalom great Ingemar Stenmark's decades-old record of 86 World Cup victories.
