The White Sox (39-47) started the second half in fourth place in the A-L Central, 13 games behind first-place Cleveland.
Guillen warned today that there will be a lot of roster changes made if the team doesn't start playing the way it should be playing.
The White Sox won the World Series in 2005 and won 90 games last year, but this season they haven't been at .500 since June First.
However, Chicago entered the break with a run of ten wins in 15 games, and Guillen expected continued improvement in the second half.
After facing the Orioles in a four-game series, the White Sox travel to Cleveland and Boston.