Burnett has already announced his plans to retire after the season, and because of that, he refuses to undergo season-ending surgery.
The right-hander was placed on the disabled list last Thursday after allowing a season-high seven earned runs in a 15-5 loss to the Cincinnati Reds. He has a 10.13 ERA in three starts since the All-Star break, and a 6.60 ERA in his last five outings.
This could present a huge challenge for the Pirates to get into the playoffs, as they are five and a half games behind the St. Louis Cardinals in the NL Central. Despite leading the wild card race, they have teams like the Chicago Cubs, San Francisco Giants, and Washington Nationals breathing down their necks.
With Burnett in the rotation, the Pirates' starters rank fourth in the majors with a 3.33 ERA, trailing the Cardinals, Los Angeles Dodgers, and Oakland Athletics. The rotation is also tied for third in the majors with 64 quality starts in the first 104 games with Burnett.
Pittsburgh will now have to look for Gerrit Cole and Francisco Liriano to lead the front of the rotation, Charlie Morton and Jeff Locke to remain consistent, and someone like J.A. Happ or Joe Blanton to take Burnett's role in the playoff race.