Morrison said he hurt the hamstring again shortly after the Mariners headed out on their last road trip.
"It was getting better, but I was running the bases and felt it pull again, so I'm kind of back to where we were," Morrison said Thursday. "I'm in the pool and walking the treadmill and stuff like that. So I'm progressing again and hopefully soon I'll be back to running and after that back out there playing. It's been a while."
Morrison said he was still only running at about 70 percent speed when he reinjured his leg.
"We did an MRI and it actually was worse than originally diagnosed," Morrison said. "But it'll be alright, eventually."
Morrison had 23 home runs and 72 RBIs for the Marlins in 123 games in 2011, but played just 93 games in '12 and 85 in '13 while dealing with a pair of knee surgeries.
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB as well as his Mariners Musings blog. This story was not subject to the approval of Major League Baseball or its clubs.