Solo told Portuguese publication Expresso that Blatter "grabbed my ass" at the ceremony. Blatter denied the accusation.
"I had Sepp Blatter grab my ass," Solo told Expresso. "It was at the Ballon d'Or, right before I went on stage."
Solo was at the ceremony to present teammate Abby Wambach with the women's player of the year award.
"I was in shock and completely thrown off," Solo told the Guardian. "I had to quickly pull myself together to present my teammate with the biggest award of her career and celebrate with her in that moment, so I completely shifted my focus to Abby."
Blatter was banned by FIFA in 2015 after a 17-year run as president. The now 81-year-old, who had his tenure come to an end amid corruption charges, in 2004 suggested women's players could wear "more feminine clothes" such as "tighter shorts."
"While in this instance it was Sepp Blatter, who was the most powerful man in football at the time, sexual harassment and inappropriate behavior are rampant at every level in women's sport, and it needs to stop," Solo told The Guardian.