The Blue Jays made the move Saturday.
The 30-year-old Romero was in the final season of a five-year contract. He had been working out at the Blue Jays' spring training complex in Dunedin.
"We made the determination we just didn't think by the end of the year he was going to be able to factor for us up here," general manager Alex Anthopoulos said. "We felt it was best just to give him the opportunity to get a head start somewhere else. It was the right thing for him."
Romero went 13-9 as a rookie in 2009 and was an AL All-Star in 2011. He is 51-45 with a 4.16 ERA overall.
Romero pitched in just four games in 2013 and spent last year in the minors.
"He's worked tremendously hard," Anthopoulos said. "We don't have any complaints."