CHICAGO -- Jon Lester said on Monday that he wanted to make his next start as planned. While the Cubs surely appreciate that mentality, the veteran pitcher will have to endure what the team hopes is a brief stay on the injured list.

Prior to Wednesday night's game against the Pirates, the Cubs placed Lester (left hamstring strain) on the 10-day injured list and promoted left-hander Tim Collins from Triple-A Iowa to give the bullpen an extra arm for a few days. Manager Joe Maddon announced that right-hander Tyler Chatwood, who is currently in the bullpen, will take Lester's spot as Sunday's starter against the Angels.

"We're not going to create a finish line," Maddon said of Lester's timetable. "Jon's a pretty tough individual, and we're just going to keep it open-ended. And as he progresses, we'll try to create the finish line. So for right now, of course he's going to miss this next start, of course he is. We know that. But beyond that, we're just going to keep an open mind."

A silver lining to the situation for the Cubs is that the team will only need a fifth starter for Sunday and April 27, considering there are upcoming off-days on April 18 and 22. Lester would be eligible to be activated on April 19, but the schedule offers Chicago the option of taking a conservative approach. If any games were impacted by inclement weather, it would also play into the Cubs' hands for utilizing a four-man rotation until Lester is deemed ready.

"We could avoid having to use that spot just based on off-days," Maddon said. "And if the weather begets some rainouts in there -- which we don't want -- but if it were to happen, other things could happen, too. Honestly, with Jon, when he's ready to go, he's going to go. That's pretty much what it's going to be."

The top option for Sunday would have typically been left-hander Mike Montgomery, but he is on the 10-day injured list with a left lat injury and is not eligible for activation until Monday at the earliest. The next alternative was Chatwood, who has not worked more than two innings in a game since March 6 during Spring Training.

The healthy starting options from the Minor Leagues who are on the 40-man roster include Duane Underwood Jr. (Triple-A Iowa) and lefty Justin Steele (Double-A Tennessee) -- Nos. 25 and 8, respectively, in the system. Righty Alec Mills is also on the 40-man roster, but he is building up his innings in Arizona after dealing with a neck issue late in Spring Training.

Collins joins bullpen
The Cubs signed the 29-year-old Collins to a Major League contract on March 24 and promptly optioned him to Triple-A to give the big league bullpen another layer of experienced depth. In nine Spring Training appearances between the Twins and Cubs this year, the lefty had 14 strikeouts against three walks with a 4.82 ERA. Collins made 38 appearances for the Nationals last season, posting a 4.37 ERA in 22 2/3 innings.

In parts of five seasons with the Royals and Nationals, Collins has turned in a 3.62 ERA in 266 games, limiting left-handed batters to a .224 average.

Worth noting
• Kris Bryant has been off to a tough start offensively over the Cubs' first 10 games, but Maddon noted that he has had positive hitting discussions behind the scenes with the star third baseman. Maddon said he does not want to ever get in the way of hitting coach Anthony Iapoce, but he will offer his own suggestions to hitters when appropriate.

"The primary thing is that he stays tall and he's not folding over," Maddon said, "and that when he hits the ball, he's hitting the ball well through the middle of the field. That's when he's normally at the top of his game. ... I've already had different conversations with K.B. about all of this. He's definitely aware."

• Former Cubs pinch-hitting specialist and fan favorite Tommy La Stella will return to Wrigley Field with the Angels this weekend for a three-game series. Maddon joked that Chicago added an extra lefty reliever to handle La Stella, who entered Wednesday with three home runs in his last two games for Los Angeles.

"We have to double down on the lefties with Tommy coming into town," Maddon quipped. "It may not help."

• Montgomery played catch out to 120 feet with no issues prior to Wednesday's game and is tentatively planning on throwing off the mound in a bullpen session on Thursday. If that workout goes well, the left-hander is hopeful that he might be cleared for activation on Monday.