The Braves announced the move Wednesday before the start of a two-game home series against the Toronto Blue Jays.
Walden was acquired from the Los Angeles Angels over the winter. He was 1-1 with a 4.85 ERA in 14 games before he went on the 15-day DL with shoulder inflammation.
Rasmus struggled in his first two big-league appearances. He allowed five runs and three homers in 3 2-3 innings for a 12.27 ERA. He gave up a double to his older brother, Colby Rasmus, in Monday's game at Toronto.
Cory Rasmus says he jokingly told his brother: "That was an awesome swing, but did you have to do it against me?"