But will Lackey be the long man out of the bullpen, or off the NLDS roster completely?
Cubs President Theo Epstein said they won't announce the final roster until Thursday.
"We're certainly looking at him as a viable option in the pen, but we're not prepared to announce the roster yet," he said.
It's really a no-brainer though, considering Lackey's status on the team and the possible need for another starter because of Arrieta's recovery from a hamstring injury.
"Jake had a great day today," Epstein said of Arrieta's bullpen session. "But you're always looking for as much depth as possible, but that's on both sides of the ball, how to squeeze it all on the roster."
Lackey didn't seem too upset during the afternoon workout at Wrigley Field, though it should be noted there were no umpires around for him to sneer at.
He made one relief appearance in the final game of the regular season, which suggests he will be sitting out there again in October. Whether he will be dancing like the rest of the Cubs' relievers is a topic for another day.
When asked about the possibility of moving to the pen in July, when he was struggling with a 5-9 record and 5.20 ERA, Lackey replied: "That ship has sailed. That ain't gonna happen. There are two places for me to be: starting or at home, except for the playoffs. In big games we can compromise."
With Arrieta's hamstring still a question mark, it would appear that compromise was reached. By slating Arrieta for Game 4, the Cubs will give him more time to heal, and if the injury affects him then Lackey would be ready to step in early on.
How difficult is it to go from starter to reliever at this time of year?
"I've seen 'Lack' come out of the bullpen and get a hold in a World Series game before," Lester said. "That's one person I'm not worried about."
The game Lester was referring to was Oct. 27, 2013, when the Red Sox were trailing the Cardinals 2-1 heading into Game 4. Lackey entered in the eighth inning with the Red Sox leading 4-2, after starting and getting the loss in Game 2.
Cardinals catcher Yadier Molina reached second on a one-out error and advanced to third on a wild pitch. Lackey then retired Jon Jay on a popup to shortstop and David Freese on a groundout to escape the inning.
The Red Sox won, and Lackey took the mound again in Game 6, allowing one run in 62/3 innings, throwing 105 pitches while notching the victory in the Series-clinching game.
The Cubs have a tight-knit team, and everyone has stuck behind Lackey despite the criticism he has received in the media for his in-game meltdowns and ornery demeanor. The rotation as a whole has had its ups and downs this season, but if the Cubs plan on winning this thing the group will have to be at the top of its game.
Lester set the tone by praising the decision to give Hendricks the Game 1 start instead of him, despite his reputation as one of the best postseason starters of his era.
"We're a unit as our starting staff," Lester said. "I'm not by any means mad. I wasn't going to be a Game 1, opening day starter the rest of my career. At some point you have to take it over."
Lester recalled "back in the day when the torch was kind of passed to me to do that."
As for Hendricks, he added: "It's a cool thing for him."
Manager Joe Maddon said Hendricks was "at the top of his game," and Lester's last two outings showed "he is coming on" at the right time.
"We could've done it another way," he said. "Absolutely. We just chose to do it this way right now. … I have so much confidence in Jon Lester pitching in the postseason, period."
The Cubs headed to Washington on Wednesday with a good feeling, knowing they're considered the underdogs in the NLDS but playing their best ball.
Being the hunter instead of the hunted is fine with everyone, despite their "embrace the target" mantra from 2016.
"In my opinion we're the favorites to win it all again," Anthony Rizzo said. "In Bryce Harper's opinion, they're the favorites, and in (Cody) Bellinger's opinion (the Dodgers) are the favorites.
"So everyone is a favorite. You just have to go out and play."
Lester agreed, and said he likes the idea of the Nationals being the favorites.
"That's the fun part about this time of year," he said. "I think everybody is the favorite to win. If you don't think you should win, then you probably shouldn't be here.
"It's exciting. It's fun and obviously everybody in (our) clubhouse thinks we should win."
Epstein said the Cubs are "just excited to play October baseball," no matter who is the favorite.
"A lot of that stuff, whether you limp in or sprint in, is out the window with how you execute the first few innings of Game 1," he said. "That starts to set the tone for the series."