Zambrano (5-6, 4.64 ERA) returned to Venezuela to be with an ailing nephew after his start Tuesday against the Nationals.
Meanwhile, Carlos Silva threw 50 pitches over 2 2/3 innings in his rehab start Friday night for Class A Peoria. Silva gave up two hits, both singles, and struck out one. The right-hander, who is 10-5 with a 3.92 ERA, has not started for the Cubs since Aug. 1, when he came out of a game against the Rockies after four batters because of an abnormal heart rate. He underwent a procedure Aug. 9 to correct that.
The right-hander was expected to throw 45 pitches over three or four innings for the Minor League team.