Valdez was removed from Friday's contest against the Cubs with left hamstring discomfort, Aiden Stepansky of MLB.com reports.
Lowe is not in the lineup for Friday's game against the Cubs.
The Pirates optioned Simon to Triple-A Indianapolis on Friday.
The Pirates activated O'Hearn (quadriceps) from the 10-day injured list Friday.
Dotel is slated to start Friday's game against the Cubs at Wrigley Field, Dominic Campbell of SI.com reports.
Cruz went 3-for-4 with a home run and an additional RBI in Thursday's 2-0 win over the White Sox.
Jones (4-6) earned the win over the White Sox on Thursday, allowing one hit and issuing two walks while striking out eight batters over seven scoreless innings.
Montgomery earned a save against the White Sox on Thursday, allowing one hit and striking out one batter over one scoreless inning.
Valdez isn't in the lineup for Thursday's game against the White Sox.
The Brewers recalled Stallings from Triple-A Nashville on Thursday, Todd Rosiak of the Milwaukee Journal Sentinel reports.
