The right-handed veteran's rehab assignment goes through June 5 which will force Texas to make a decision, barring another injury requiring more DL time.
He can't continue to pitch on a rehab assignment once the 60-day period concludes June 5.
Rangers general manager Jon Daniels said the club is still evaluating whether to add Lincecum to the roster. He's scheduled to pitch for Triple-A Round Rock Friday and Saturday.
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Lincecum has allowed runs in five of his six relief appearances since joining Round Rock on May 7. He's allowed eight hits and walked six in 8 1/3 innings. He also has eight strikeouts.
Lincecum, who signed with the Rangers in March, was slowed by a blister on his right middle finger.
"The staff in Round Rock has said his stuff has gotten better," Daniels said. "He's gotten more comfortable and a little more consistent. His changeup is probably his best swing-and-miss pitch. He's done a better job of getting ahead with the fastball to set that up."