When asked after Tuesday's 5-2 loss to Seattle whether he would return to the Phillies in 2015, Burnett said, "Probably not. We'll see."
Burnett (6-14) has signed a one-year deal with a player option for 2015 before this season. He can max out his current deal at $12.5 million with five more starts.
The veteran right-hander lost his fifth straight decision Tuesday and dropped to 0-6 with a 6.41 ERA in seven starts since the All-Star break. He allowed six hits with four walks and hit two batters in 7 2/3 innings versus Seattle.
Burnett, 37, has a career record of 153-146 with a 4.02 ERA and 2,325 strikeouts over 15 major league seasons.
The Associated Press contributed to this report.