Cubs starting pitcher Cole Hamels threw a few warmup pitches before the bottom of the second inning Friday night in Cincinnati and didn't even hesitate before walking off the mound and straight down through the dugout and into the clubhouse. He motioned to catcher Willson Contreras as he was walking off as if to say "I'm done." 

During the third inning, the Cubs announced that Hamels felt something in his left side and he's still being evaluated. After the game, manager Joe Maddon confirmed Hamels was heading to the injured list with a strained oblique:

No matter how much time Hamels does miss, the Cubs' tenuous depth in the rotation gets tested even further than it already has. 

Hamels has been the Cubs' best pitcher to this point in the season. In the month of June, heading to Friday, Hamels had a 1.00 ERA, 0.89 WHIP and 36 strikeouts against eight walks in 36 innings. He went at least seven innings in all five starts (again, prior to Friday). On the year, he was 6-2 with a 2.92 ERA (154 ERA+), 1.19 WHIP and 96 strikeouts in 98 2/3 innings. He had a chance to make his first All-Star team since 2016 and I suppose he still does, but he'd need to be replaced. 

Kyle Hendricks -- who has been the second-best -- is on the injured list due to right shoulder inflammation. If Hamels hits the injured list, here's what the Cubs are left with as viable rotation options: 

  • Jon Lester. He's 35 years old and has been a mixed bag this season. He was awesome to start (1.16 ERA through seven starts), but just had a seven-start stretch where he had a 7.17 ERA. He did have a good outing last time out. 
  • Jose Quintana. The lefty had a 3.30 ERA through 10 outings, but he's posted a 6.75 ERA since (six starts). 
  • Yu Darvish. He hasn't been quite as bad since he quit walking so many guys (5.40 ERA through eight starts; 4.70 since), but he leads the league in walks and home runs allowed. He's already started 17 games, so it's past the point where we can talk about small-sample flukes. He's not reliable at all. 
  • Tyler Chatwood. He had a good spot start early in the season, but his last two outings have been starts and he's allowed nine runs (eight earned) on 12 hits and five walks in nine innings. He shouldn't be in a rotation on a contender. 
  • Mike Montgomery. He's generally been fine for the Cubs as a starter in 2017-18, but hasn't yet started this season and has had hard contact issues this season. He also shouldn't be in a rotation on a contender. 
  • Adbert Alzolay. The kid has electric stuff. Through 8 2/3 innings in his MLB career, he has nine strikeouts and a 2.08 ERA (his two allowed runs were solo homers). He has the talent, but both games ran out of gas in his fifth inning of work and -- due to injury -- he only threw 39 2/3 innings last season in Triple-A. He's good enough to be in a rotation, but workload concerns are going to limit him. 

The Cubs need both Hendricks and Hamels back ASAP, because Quintana and Darvish need to be the 4-5 starters with Alzolay as a spot starter/late-inning reliever until he moves into the rotation next season. It's possible Hendricks is ready to return and slots into Hamels' spot in the rotation until the All-Star break and then Hamels can return after the break. That seems like the most realistic positive answer the Cubs could hope for with this situation. 

The doom-and-gloom scenario has both Hamels and Hendricks out for several more weeks, in which case it's hard to see the Cubs holding onto first place. That rotation above just isn't good enough. 

The Cubs entered Friday night with a one-game lead in the NL Central.