The 2008 AL Cy Young Award winner felt so good during his second bullpen in three days that he threw 63 pitches -- about 10 more than planned.
Lee has been out with a strained abdomen since March 15. Pitching coach Rick Adair said Tuesday that pain is no longer an issue and Lee just needs to build his endurance.
Lee is expected to throw a simulated game Friday and make at least one minor league rehabilitation appearance.
He also has a hearing Wednesday for his appeal of a five-game suspension for throwing over the head of Arizona's Chris Snyder during the spring game in which he was injured.