Magill walked nine and allowed four home runs in the Dodgers' 7-2 loss to the Rockies.
The club said it believes Ryu can start Thursday or Friday. Ryu threw a rare bullpen session Monday to test the foot.
Ryu took a line drive off the top of his left foot in the fourth inning during his first complete game shutout in his Major League Baseball career against the Los Angeles Angels on Tuesday.
The Dodgers had expected Ryu to make his scheduled start on Sunday, saying that X-rays on his foot were negative.
Ryu is 6-2 with 2.89 ERA and 67 strikeouts in 71 2/3 innings.
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