Rusin made one start on Tuesday against the Brewers, and gave up one run on one hit over five innings.
"He can make the ball do a lot of things," Cubs manager Dale Sveum said of Rusin. "He has a plus changeup and keeps the ball down. You'd like to see him in another environment where it isn't his first start, too, where all the jitters are gone and all that. He'll be the first to say his command wasn't the greatest, but he battled back and got back into counts -- and made the pitches and kept the ball on the ground when he had to. He's definitely a guy you want to see more of."
Saturday was Raley's fourth big league start. He picked up his first Major League win in his last outing on Aug. 18 against the Reds.
While Rusin was expected back on Sept. 1, Sveum said the Cubs wouldn't add too many others. Most of the top Minor League players are already on the roster.
"I think it'll be just enough to help us out in September to where we can do some things roster-wise in the game and pinch-hit," Sveum said. "We're not going to bring 15 guys up or anything like that.
"Most of them are here anyway. There are some guys coming back from injuries who we still want to take looks at."
That would probably include right-hander Blake Parker, who has been rehabbing at Iowa from a stress reaction in his right elbow.