MESA, Ariz. -- With lingering concerns over Brian Duensing's back spasms, the Cubs placed the reliever on the 10-day disabled list to start the season and will break camp with both outfielder Matthew Szczur and infielder Thomas La Stella on their 25-man roster, president of baseball operations Theo Epstein announced Wednesday ahead of the team's final spring game in Arizona.
That leaves the club with seven relievers among its 12-man pitching staff, and 13 positional players.
Duensing, who pitched two innings against the Giants on Tuesday, missed two weeks in early March with back spasms, and the lack of innings and repetition prompted the Cubs to exercise caution in his return. He will begin the season on a rehab assignment with Triple-A Iowa, and his placement on the DL is retroactive to Wednesday.

"We want him to have the benefit of a full spring, just to make sure he's ready, and then also put him in position to have a good season for six, seven months," Epstein said.
The Cubs have three days off during their first eight-game stretch, which tempers urgency in their bullpen. Mike Montgomery will be the lone left-handed reliever on the Opening Day roster. He's joined in the bullpen by Wade Davis, Hector Rondon, Pedro Strop, Justin Grimm, C.J. Edwards and Koji Uehara.

"Usually throughout baseball history, a seven-man 'pen has been more inadequate," Epstein said. "But certainly for us early, with the off-days, we should be OK."
The move created an extra bench spot in what was thought to be a choice between Szczur and La Stella, a pair of seasoned veterans who had productive camps.
Szczur was out of options, and would have been at risk to be picked up by another club had he been sent to Triple-A Iowa. Szczur is batting .295 with an .831 OPS in 44 at-bats this spring, and was in the lineup Wednesday against the A's. La Stella hit .270 with an .835 OPS in 37 Cactus League at-bats.
Russell to play Thursday in Houston
Manager Joe Maddon said Addison Russell (stiff lower back) is slated to return Thursday in an exhibition game against the Astros at Minute Maid Park.
Russell, who has thrown the last three days and will swing for the second consecutive day, hasn't played since March 22. He may face live pitching Wednesday, depending on pitchers' availability.
"Today it's about 100 percent. I feel confident," Russell said. "This morning, I shot up early. I didn't even really think about my back whenever I woke up. I just kind of got up and sprung up out of bed. That's always a good sign."

Maddon said he believes Russell is in better physical shape than he was last spring. Maddon also said it wouldn't be necessary for the starting shortstop to play both games in Houston to ensure he's prepared for Sunday's season opener against the Cardinals. Five of Russell's nine hits in 32 at-bats this spring were homers, and he's posted a 1.142 OPS.
"I just want to make sure that he feels good, more than anything, about his swing," Maddon said. "He was doing so well at the plate. That's my only concern -- that rhythm is off a little bit."
Worth noting
• Epstein said left-hander Rob Zastryzny, who was optioned to Triple-A on Monday, will be used as both a starter and reliever to start the season. Zastryzny will follow a similar throwing pattern to last year, Epstein said, which began with 19 consecutive starts between Double-A and Triple-A, with 80-90 pitches per outing. In his limited stint with the big-league club last year, Zastryzny posted a 1.13 ERA with 17 strikeouts in 16 innings, including one start.
• The Cubs remain in talks with Munenori Kawasaki about returning on a Minor League deal, Epstein said. They released Kawasaki on Tuesday to allow the infielder to seek other opportunities, largely due to the middle-infield depth the Cubs have with Javier Baez and Benjamin Zobrist. Epstein said Kawasaki could be the starting shortstop at Iowa if he decides to return.
• Wednesday's crowd of 15,448 brought the Cubs' Cactus League attendance total to 226,933 to set an MLB single-season Spring Training record. The Cubs also hosted two World Baseball Classic exhibition games, against Italy on March 7 and Japan on March 18, to bring the Sloan Park 2017 total to 251,899.