Solo, 37, told the BBC that Ellis "cracks under pressure" and the U.S. team wins in spite of Ellis' coaching methods.
"She's not the leader I wish her to be," Solo said. "She relies heavily on her assistant coaches. ... But oftentimes it doesn't matter, because the quality of the players on the U.S. team is superb."
Solo and Ellis, who was named the U.S. national head coach in 2014, have feuded for several years. Solo was suspended for six months and later had her contract terminated after calling Sweden's national team a "bunch of cowards" during the 2016 Summer Olympics in Rio de Janeiro.
Solo was the goalkeeper for the 2015 World Cup-winning squad. She also earned gold medals as the goalie for the 2008 and 2012 U.S. Olympic teams.
"We have a rich history of winning, a winning tradition, and it doesn't matter oftentimes who's coaching us, because we'll find a way to win ... in spite of who the coach is," Solo said.
The United States begins the Women's World Cup by playing Thailand on Tuesday. The match will be played in Reims, France.