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.
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."