The move was made retroactive to Tuesday. Ankiel, batting .247 with two home runs and 11 RBIs, has a bruised right shoulder and overall soreness related to the collision. Manager Tony La Russa expects him to be ready to return once he comes off the DL.
La Russa said the move was made to allow Ankiel to pace his rehab instead of pressing to return. The bench is already short a position player because of La Russa's decision to go with a 13-man pitching staff during a string of 20 straight games without a day off.
"He's sore enough to where by the time he's ready to participate there will be enough days where he's unavailable and we're playing short," La Russa said. "It takes all the pressure off him trying to hurry because he's conscientious, so he'll get two weeks to get 100 percent."
Outfielder Shane Robinson's contract was purchased from Triple-A Memphis, giving the Cardinals 39 men on their 40-man roster. Robinson, 24, was batting .345 with two RBIs and 13 runs in 15 games in the minors.
Robinson was a fifth-round pick in the 2006 draft out of Florida State.
"In camp he was the complete thing, tracked the ball well at all three spots," La Russa said. "At the plate, he really has the kind of stroke that gets your attention.
"He'll put a charge in the ball and I'm anxious to see him play," he said.
Rookie Colby Rasmus got his third straight start in center field Thursday in place of Ankiel. The Cardinals had been rotating four outfielders all season before Ankiel's injury, along with left fielder Chris Duncan and right fielder Ryan Ludwick.
The Cardinals originally said infielder Brendan Ryan, out with a strained left hamstring since April 29, would begin a rehab assignment Friday at Class A Quad Cities. But trainer Barry Weinberg decided Ryan was not yet ready.