The team said Tuesday that Waechter's placement on the DL is retroactive to April 18. The Royals said he has a lateral strain in his right elbow. The 28-year-old has a 4.50 ERA in three relief outings.
Bannister is 0-1 with a 3.46 ERA in three starts for Omaha. The 28-year-old is scheduled to make his first start with Kansas City on Wednesday night at Cleveland.
Bannister is 3-1 with a 1.91 ERA in five career appearances against the Indians. He started 27 games in 2007 and 32 games in 2008 for Kansas City but didn't make the team in spring training.
"He was throwing well [at Omaha]," Royals manager Trey Hillman said. "It was a better fit for us."
Bannister will take the rotation spot of left-hander Horacio Ramirez, who has been sent to the bullpen. Ramirez is 0-1 with an 11.12 ERA in three appearances, including one start.
He has allowed seven earned runs and 12 hits in 5 2/3 innings. Opposing hitters are batting .429 against Ramirez.
"He wants to start," Hillman said. "I don't blame him. I understand."
Hillman said Ramirez will be used in middle relief and possibly to match up against left-handed hitters.