"When it comes down to it, injuries are injuries, but I'm pretty much the weakest link in the rotation right now and have to figure out a way to right the ship, pick my end up, and do better," Lester said, according to ESPN's Jesse Rogers. "Flat-out do better. Our rotation has pitched well, except for me."
Tuesday's loss brought Lester to 9-8 on the season.
The 35-year-old southpaw's last outing didn't fare much better. On Aug. 1 against the St. Louis Cardinals, Lester allowed five runs on nine hits in five innings pitched. The Cubs lost 8-0. By comparison, Lester allowed eight earned runs through four starts (26.0 innings) in all of July.
On the season, Lester owns a 4.46 ERA and 1.41 WHIP.
Prior to Lester's 10-run performance against the A's, the Cubs' starting rotation ranked fifth in MLB with a 3.97 collective ERA. The group's ace has been Kyle Hendricks, who holds a 3.06 ERA, 8-8 record and 1.089 WHIP.
It's Chicago's bullpen that has caused the most concern, and the pitching staff took a hit to start the week by placing closer Craig Kimbrel on the 10-day injured list Monday with right knee inflammation and then sending Brandon Kintzler to the 10-day IL after he suffered pectoral inflammation while filling in for Kimbrel that night.
Lester led the National League with 18 wins last season, so the ability is there. The 61-52 Cubs will welcome his top form reappearing soon as they hold a tight 2.5-game lead over the Cardinals in the NL Central.