At least for now, let’s take Jon Lester at face value when he says he won’t be out long:
Lester was sidelined with a lat strain in 2011, but he said this wasn't as severe, and he expected to be out a minimum amount of time.
"The big thing is the overall performance wasn't there," Lester said. "It's something we've tried to manage for a while and get through. It got to a point where you're doing a disservice to your team by not being able to perform.
"It [stinks] going on the DL, but at the same time, I wasn't helping going out there."
Lester didn't want to predict when he'll return.
"I don't expect it to be long, but that being said, I don't want to put a timetable on it either," he said. "Obviously, the quicker the better, but I don't know. We'll play it by ear."
That article also quotes Cubs GM Jed Hoyer as saying that Lester’s arm is “tired,” and quotes Joe Maddon as saying he noticed a drop in Lester’s velocity.
Looking at Lester’s 2017 Fangraphs page, the velo drop is confirmed. He was averaging 92 miles per hour plus on his fastball as recently as a month ago, but just 90.7 in the brief, two-inning outing against the Reds. Look at the 89 mile per hour “fastball” he pretty much laid in there to Joey Votto Thursday:
The Cubs have the benefit of an off day Monday. If they choose, they can go with John Lackey Tuesday against the Reds in Cincinnati, and then Jake Arrieta and Jose Quintana on normal, four-day rest Wednesday and Thursday to wrap up that series.
Kyle Hendricks, who’s going Sunday against the Blue Jays, could then go on four days’ rest Friday, August 25 in Philadelphia.
The next time the Cubs actually would need a starter beyond those four is a week from today, August 26 against the Phillies. Right now, it looks like Mike Montgomery will make that start, according to this article, though management didn’t commit to any specific date when noting that Montgomery will fill in for Lester. August 26 would be eight days after Lester was placed on the disabled list, so conceivably, he could be back August 31 to make a start at Wrigley Field against the Pirates.
Or, he could be held out of the rotation for one more turn and face the Pirates in Pittsburgh September 5, if he’s ready by then. Also by then, rosters will have been expanded and there will surely be a couple of extra arms in the bullpen.
Friday, I wrote about the possibility of exploring the acquisition of Justin Verlander if Lester was going to be out for the year. Since that doesn’t appear to be what’s happening with Lester, I think the Cubs can put a Verlander acquisition on the back burner... for now. It’s something I do think they should look into over the offseason. Like Arrieta, Verlander has gotten better as the season has gone on. His last eight starts: 2.55 ERA, 1.057 WHIP, 58 strikeouts in 53 innings.
Whether it’s a lat strain (something Lester spent a bit of time on the DL in 2011 for) or just plain old dead arm or fatigue, it doesn’t sound like the Cubs will be without Lester for too long. And that’s surely good news.