The right-hander came out of Thursday's game against Texas after facing one batter. An MRI was negative.
"Opening day is out of the question for him now," Cubs manager Dale Sveum said Saturday.
Mateo pitched in 23 games was 1-2 with a 4.30 ERA in 23 games for the Cubs last season before going on the disabled list July 5 because of a sore elbow. He didn't pitch again during the rest of the season.
He is 0-2 with a 7.50 ERA in six innings during spring training.