Weather delays slowed the right-hander's arrival on Saturday from Memphis, Tenn., where Triple-A Iowa was playing. He did arrive in time for the Cubs' Interleague game against the White Sox.
To make room on the roster, left-hander James Russell was optioned to Iowa. Russell was 0-1 with a 4.71 ERA in 20 relief appearances.
"We need a pitcher in here with a fresh arm," Cubs manager Lou Piniella said Saturday.
Atkins had been scheduled to start Friday for Iowa but Jeff Samardzija got the assignment, his first start of the season, and gave up one hit in four innings in a 4-1 win. In 17 games this season at Iowa, Samardzija is 4-0 with a 2.16 ERA. He's walked 17 and struck out 22 in 25 innings.
The Cubs' bullpen is shorthanded because the starters went five innings in each of the past three games.
John Grabow also could rejoin the Cubs' bullpen soon. The left-hander was placed on the disabled list June 8 with a sore left knee and in two rehab starts with Iowa, he's given up one hit and one walk and struck out one in two innings.