Acquired from the Marlins in a December trade for reliever Carter Capps, Morrison could be an option in the outfield, at first base or designated hitter. But with an already lefty-heavy lineup, the thinned-down Morrison will have to earn his playing time by producing with the bat for a team searching for middle-of-the-order support behind new second baseman Robinson Cano.
The 6-foot-3 Morrison was listed at 248 pounds last year by the Marlins, but weighed 224 pounds when he took his physical with the Mariners six weeks ago.
"I don't really care what my weight is, as long as my body and knee feel good," he said. "I'm hitting in the cage and the ball seems to be coming off my bat well."
Morrison hit .247 with 23 home runs and 72 RBIs as a rookie outfielder for the Marlins in 2011 and was regarded as one of their rising stars, but knee problems literally took the legs out from under his efforts the past two years.
After having patella tendon surgery, he got just 15 at-bats in Spring Training 2012, then tried playing through pain until finally shutting it down in late July after hitting .230 with 11 homers and 36 RBIs in 93 games.
Following a second surgery on the same knee, Morrison missed all of last year's Spring Training and the first nine weeks of the season before returning to hit .242 with six homers and 36 RBIs in 85 games while being limited to first base.
The sense now is that he rushed to come back too quickly in 2012 and wound up hurting himself again, thus turning a one-year issue into two unhappy seasons.
"I just wasn't ready to go," he said. "It was probably mostly my fault, but that's in the past now."
So when Morrison talks about a fresh start with the Mariners, he's not just speaking of a new team in a new league on the opposite corner of the country from the Marlins.
"I'm just coming in in the best shape as I can," he said. "I don't care where I play, as long as I'm in the lineup. I want to play every day. I don't care whether it's DH or catcher -- well, hopefully it's not catcher or we'll be in trouble. But left field, right field, it doesn't matter."
Morrison is a character who enjoys interacting with fans in person or on Twitter, where he has more than 122,000 followers on his @CupOfLoMo account.
He at times irritated Marlins management with his irreverent tweets, but has kept things pretty low key since his trade to Seattle.
"I just haven't been on it as much," Morrison said. "It's nothing that has changed. I just go in spurts with it. I get tired of it and then I get on there. I get tired of it and then I get on there. I am getting a lot more 'Are you a Seahawks fan?' questions now."
Morrison, who lived in Denver this offseason, indeed rooted for Seattle in the Super Bowl. But he's concerned now solely with getting himself prepared for his first healthy spring in three years.
"There's something to be said for having Spring Trainings and getting the kinks out and starting when everybody else starts," he said. "It's not just the game itself and getting back into the swing of things, it's more for just the mental side of starting when everybody else starts, being on the same level as them and not having everybody else have a head start. So I'm excited about it."
As for his once-balky knee? He says his offseason workouts have been full bore.
"The body is good to go. The mind is never 100 percent," he said with a laugh. "I've always got problems there. But the body is great."