Ottavino threw 30 pitches from the mound in a pregame workout and hoped to be available in the bullpen. After seeking a second opinion, he opted for rehab rather than undergo a procedure that could have sidelined him for 10 months.
Ottavino has been on the 15-day disabled list since early July. The team had initially announced that Ottavino, 0-2 with an 8.46 ERA in five games including three starts, would undergo season-ending surgery.
Manager Tony La Russa said Ottavino's progress was encouraging and he could use a pitcher now that the team is without Adam Wainwright and Blake Hawksworth. Wainwright has been shut down with a right forearm strain and Hawksworth was struck in the face by a line drive Saturday in Chicago.
But the manager said he'd wait to see how Ottavino, the team's first-round pick in 2006, feels the next few days.