NEW YORK -- With every game critical in a close playoff race, the Chicago Cubs are moving struggling left-hander Drew Smyly to the bullpen.

Rookie right-hander Javier Assad will take Smyly's spot in the rotation this weekend at Toronto, which features several right-handed sluggers in a lineup battering lefties lately.

Smyly is 8-8 with a 5.05 ERA in 23 games this season, including 21 starts. He is 0-4 in his last six starts since June 28, with his only win during that stretch coming in relief July 28 at St. Louis.

Chicago manager David Ross said Smyly will provide length in the bullpen but probably won't stay there for long.

"I don't know that he needs a real mental break," Ross said. "I think it's just one of those things, it's an opportunity for him to help us out of the 'pen while he's not throwing his best, and Javy slots in who is throwing really well."

Smyly was tagged for seven runs and eight hits over five innings Monday night in an 11-2 loss to the New York Mets.

"He wants to win just like everybody else. He gets it. With our off days, it makes a lot of sense," Ross said. "There's some, you know, Toronto and what they've done to lefties, especially over the last couple of months, has been pretty impressive. And so, trying to take the best matchups and give ourselves a chance to win is what we're trying to do -- maximize every number we can and matchup we possibly can to give us any kind of slight edge going into each series, and this is just one of those things."

Assad is 1-2 with a 3.35 ERA in 18 relief appearances and two starts this year. He started Saturday at home against Atlanta and threw 83 pitches over 3 2/3 innings while allowing two runs and five hits.

Before that, Assad threw 62 pitches in relief July 31 against Cincinnati, so he's pretty well stretched out. He will pitch Friday night against the Blue Jays in the opener of a three-game series.

After completing a stretch of 16 games in 16 days Wednesday night against the Mets, the Cubs have three of the next eight days off, giving them an opportunity to adjust their rotation.

They also hope All-Star starter Marcus Stroman (right hip inflammation) will return from the injured list when he becomes eligible Aug. 16.

"Drew will go to the 'pen for probably a short amount of time," Ross said. "He'll give us some length in the 'pen while we have those off days and then try to reassess once we get back to a regular schedule."

The Associated Press contributed to this report.