The news was first reported by People.com, and Cutler confirmed it on his Facebook page, according to the Chicago Tribune.
"Thank you all for the support, but if you talk bad about Kristin I will delete and block you," a post on Cutler's Facebook page said. "It's unnecessary and heartless. Also, don't say now I can play football, I could play football when I had her compared to when I don't. Football is the least of my worries, so have some respect."
Cutler changed his status on the site to "Single."
Cutler had popped the question to Cavallari during a romantic getaway in Cabo San Lucas in April.
Cavallari, 24, who appeared on "The Hills," and Cutler, 28, had been dating since last fall.
"She got dumped," a source told People. "She's absolutely devastated. She can't believe this is happening."