Guillen, who has been rehabbing in Miami for the past week, went on the disabled list on May 5, but had to shut down all baseball-related activities after the pain in his right shoulder refused to go away.
The team hopes that the injury will heal with rehab and physical therapy work, but hope to decide somewhere around the All-Star break if enough progress is being made to be able to count on Guillen at some point this season. If not, they may elect for season-ending surgery so that he can be 100 percent heading into 2010.
"He's making some progress," Rand said prior to the Tigers' series opener against the Cardinals. "It's been slow, but he can go through the throwing motion without any pain now. ... Not with a ball, he's not throwing yet. And he's starting to get pain-free in all of his movements, so hopefully we can start some more specific strengthening later this week, so we're kind of progressing along that timetable and we're just going to see where it takes us.
"Until you start doing baseball activities again, I can't get too excited, but he said to me today on the phone that he is feeling a lot better than when he went down there. He's encouraged by it."
B.J. Rains is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.