MESA, Ariz. -- Cubs manager Joe Maddon noted earlier this week that left-hander Brian Duensing has been spending time in the team's pitching lab to keep working on delivery adjustments. With Opening Day less than a week away, Chicago is shifting its focus to results.

On Sunday morning, the team announced that Duensing had been designated for assignment, opening a 40-man roster spot to sign lefty Tim Collins to a one-year, Major League contract. Collins was subsequently optioned to Triple-A Iowa, but the transaction brought the Cubs' Opening Day bullpen plans a little more into focus.

"This guy's been a big part of our culture and our success the last couple years," Maddon said of Duensing. "He's a big part of the maintenance of the bullpen and even in the clubhouse. He's just a really good guy to be around, and guys kind of gather towards him. So, that's missed right now.

"But, if this whole thing works out, you may see him back here again with us, as he continues to work through some stuff. Really, quite a pleasure to be around."

The 36-year-old Duensing (under contract for $3.5 million this season) will be exposed to waivers -- meaning any other team can claim him -- but could be outrighted to Triple-A if he clears and accepts the assignment.

With Duensing no longer in the bullpen competition, the battle for the last spot is down to righty Allen Webster (non-roster invitee) and lefties Kyle Ryan and Randy Rosario (both on the 40-man roster). The Cubs also are still exploring external alternatives as the season opener Thursday against the Rangers nears.

Maddon did note that there would be a benefit to having a second lefty in the Opening Day bullpen. As things stand, the lone lefty is Mike Montgomery, with Pedro Strop, Steve Cishek, Brad Brach, Carl Edwards Jr., Brandon Kintzler and Tyler Chatwood rounding out the cast.

"Yeah, it'd be kind of nice to have more than one [lefty]," said Maddon, whose club has a nine-game road trip through Texas, Atlanta and Milwaukee to start the season. "We're playing the Rangers, who are very left-handed dominant. The Braves have some really good left-handed hitters and so do the Brewers. However, the way our starters line up, we still have three left-handed starters, which kind of can ameliorate those concerns a bit.

"But, matching up during the course of the game, you just don't know how the game's going to play out. It's nice to have more than one."

Collins, 29, has spent parts of five season in the Majors between stints with the Royals and Nationals, posting a 3.62 ERA in 266 career games. Last year, the lefty split his time between Triple-A and MLB with the Nationals, turning in a 4.37 ERA in 38 big league games with a .194 opponents' average (.631 OPS) against left-handed batters across both levels combined. Collins had 12 strikeouts against three walks in 7 1/3 innings this spring with the Twins, who released the lefty.

"Collins is good," Maddon said. "He's got that elevated fastball with a really good breaking ball and cutter off of it. He can get lefties and righties out. Durable kind of a guy. Physically, he's not very tall, but I've seen him really good."

Duensing has turned in a 10.29 ERA this spring in eight Cactus League outings, allowing eight runs on nine hits with three strikeouts and two walks in seven innings. That showing comes after the left-hander posted a 7.65 ERA in 48 games for the Cubs last year -- a dramatic decline over his solid '17 campaign (2.74 ERA in 68 games).

"He put a lot of work in this offseason, trying to have a better spring to provide a better foundation for the year," Cubs president of baseball operations Theo Epstein said. "And he got bogged down with some mechanical issues. Again, you never want to evaluate in Spring Training, but you look a little bit more at the process than results and look at that in conjunction with performance from last year and try to make the right call.

"And we just felt like he wasn't in a position right now to help us. I think that, certainly, he's capable of it if he gets locked back in mechanically. That may become a situation where he's still in the organization and he can continue to work on things."