Rasmus has developed a cyst in his inner ear that is growing behind the eardrum. He recently told reporters the official diagnosis is cholesteatoma, a growth of skin cells that causes damage inside the inner ear.
Rasmus attempted to play through the issue but struggled mightily and is just 3-for-66 since July 2.
"We determined we need to get this ear thing checked out further," Astros manager A.J. Hinch told reporters. "He's not feeling very well, and it's been bothering him for a while."
Rasmus was unavailable to reporters on Sunday but previously said he will eventually need to undergo surgery. He was hoping to finish the season before having the operation.
It wasn't immediately known if the timetable will change now that Rasmus has been placed on the disabled list.
Rasmus is batting just .211 with 12 homers and 48 RBIs this season. He was hitless in 23 at-bats over his last six games played.
"He has tried his best to navigate some of the symptoms and get through his day to day, but it was clear to us that it's not going to work," Hinch said.
Ramsus hit a career-best 25 homers for the Astros in 2015.
The Astros recalled utility player Tony Kemp from Triple-A Fresno to fill the roster spot. Kemp batted .238 in 22 games with Houston earlier this season.