Chicago Cubs ace Jon Lester left his start on Thursday against the Cincinnati Reds alongside the trainer. 

Lester made some history before he exited. That's because he became the first pitcher in the last 30 years to allow multiple nine-run innings in a season:

Perhaps predictably, it was announced on Friday that Lester would hit the disabled list due to shoulder fatigue. He wasn't the only Cubs pitcher placed on the DL, either -- reliever Justin Grimm will also miss time. 

It's been a disappointing year overall for Lester, who entered Friday with a 4.37 ERA (98 ERA+) and 3.37 strikeout-to-walk ratio. He's averaging fewer than six innings per start for the first time since 2007. The Cubs have not announced who will take his spot in the rotation. Either Mike Montgomery or Eddie Butler, currently stationed in Triple-A, would make the most sense.

Grimm too has had a less-than-stellar season. He's managed a 5.40 ERA due in large part to a persistent home-run problem. In 43 innings this season, he's yielded 11 home runs. He'd allowed nine total over 102 innings split between 2014-15.

Losing Lester is the bigger blow, and the one that could prove most consequential to the Cubs' playoff chances. Though they enter the weekend in first in the National League Central, they hold just a one game lead over the Milwaukee Brewers and a 1 1/2-game lead over the St. Louis Cardinals. The Cubs' rotation has been an issue all season, and an extended absence from Lester won't help. After all, Lester leads the Cubs in innings pitched and has the best FIP among starters. 

We'll see if Lester can make his way back over the next two weeks. If not, the Cubs' Central chances will dwindle.