Burnett is wearing a walking boot over his torn right calf and isn't sure when he'll be ready to return. Burnett injured the calf while working out Wednesday and was placed on the 15-day disabled list a day later by Pittsburgh.
The 36-year-old Burnett is 4-6 this season with a 4.00 ERA. He threw a season-high 112 pitches in a win over the Chicago Cubs last Saturday but said the injury is not related. The right-hander is the fourth member of Pittsburgh's starting rotation to go on the disabled list this season, joining Wandy Rodriguez, Jeanmar Gomez and James McDonald.