DENVER — The Chicago Cubs put pitcher John Lackey on the 15-day disabled list because of a strained right shoulder.

The 37-year-old Lackey has made 24 starts this year in his first season with the NL Central leaders. He is 9-7 with a 3.41 ERA.

Lackey’s move to the DL was retroactive to Monday.

The Cubs also put right-handed reliever Hector Rondon on the 15-day disabled list with a strained right triceps. He is a 2-3 with a team-leading 18 saves and a 2.47 ERA. That move was retroactive to Wednesday.

INVESTIGATION: Philadelphia’s Ryan Howard and Washington’s Ryan Zimmerman have been cleared by Major League Baseball of allegations they used banned performance-enhancing substances.

Pharmacist Charlie Sly claimed in an Al-Jazeera America documentary “The Dark Side: Secrets of Sports Doping,” which was broadcast Dec. 27, that the two used banned performance-enhancing substances.

In a brief statement Friday, MLB said its investigation “did not find any violations of the Joint Drug Prevention and Treatment Program by either Howard or Zimmerman.”

MARINERS: Seattle optioned slumping first baseman Dae-Ho Lee to Triple-A Tacoma.

Lee, a star in South Korea and Japan, was a revelation the first half of the season, earning his way into a regular platoon at first base. He’s been in a slump since the All-Star break, hitting just .109 with one homer and four RBI in 20 games.

DODGERS: Injured left-hander Clayton Kershaw joined Los Angeles in Cincinnati and threw on flat ground, the last step before he throws off a mound for the first time in more than a month.

ROCKIES: Colorado reinstated reliever Chad Qualls from the 15-day disabled list and cleared a roster spot for him by optioning struggling rookie reliever Carlos Estevez to its Triple-A affiliate in Albuquerque.