The move is retroactive to July 14.
To take his place on the roster, the team selected the contract of infielder Ben Paulsen from Triple-A Colorado Springs. The Rockies also designated right-hander Jair Jurrjens for assignment.
Moments before the first pitch against Washington, the team announced reliever Boone Logan was placed on the 15-day disabled list with diverticulitis, a condition in which the inner lining of the intestine becomes inflamed or infected. Nick Masset (strained left patellar tendon) was reinstated from the DL to take Logan's place in the bullpen.
Paulsen, 26, made his major league debut at first base Monday against the Nationals.
Morneau is hitting .312 with 13 homers and 60 RBIs. He took part in the Home Run Derby at the All-Star Game in Minnesota.
All-Star shortstop Troy Tulowitzki was out of the starting lineup for a second straight game with a tender left thigh. Tulowitzki said he still felt a "little sore" but didn't think he'd have to go on the DL.
"Numerous times in my career I've played through things like this and gotten myself in trouble," Tulowitzki said. "So it's time to be smart. And when I get back out there, that I'm able to go 100 percent."