Once a rising star, Sizemore has been plagued by a barrage of injuries and has had numerous surgeries in recent years, including microfracture surgery on both knees.
But Sizemore thinks he is ready to start spending his time on the field instead of the training table.
"So far I've been pretty much going through a normal offseason -- running, training, doing baseball stuff, throwing and hitting," Sizemore said. "When I come to camp, I should be ready to go and fit right in and just kind of get my legs underneath me and go from there."
If Sizemore can stay healthy, he at least has a chance to win a starting job. Prospect Jackie Bradley Jr. will be his top competition in center field.
"We added Grady because one, he's available; and two, it provides some competition," said manager John Farrell. "And yet we have to see once we get to Spring Training, Grady's tolerance physically. We don't have a projected number of games that we look at that he might be available for. We have to gradually build that up, build his endurance up. That's how Spring Training will be spent with him."
Following the departure of center fielder Jacoby Ellsbury, who signed with the Yankees, Boston hadn't signed another outfielder until Sizemore.
"Honestly, I'm looking for an opportunity to play. It wasn't really looking for a place for center field," Sizemore said. "It was more just looking for an opportunity to get in the outfield and fit in any way the team needed me to. I thought it was a good opportunity to be a part of the team, and I thought that it was one of those things where I was looking to fit in any way that I could."
Farrell stressed that Bradley still is very much in the running to win the job.
"It doesn't take Jackie out of the mix at all," said Farrell. "There's questions that we have to answer in Spring Training with our roster. So the fact of Grady signing and being added to our roster doesn't remove Jackie from [consideration]. I think one of the things that [general manager] Ben [Cherington] and all of us have set out to do in these final weeks before Spring Training is add to the depth of our team, and Grady certainly does that right now."
Sizemore is still relatively young at 31.
"Yeah, it's been frustrating," Sizemore said of losing so much time to injuries. "No one likes dealing with injuries, and I've had my fair share. You know, hopefully that's behind me now, and I'm looking forward to just kind of moving on and starting the second half of my career."
As the farm director of the Cleveland Indians from 2001-06, Farrell had considerable history with Sizemore. In fact, when Bradley was having a standout Spring Training in 2013, Farrell was asked to compare him with Sizemore.
"Similar temperament. Nothing was ever taken for granted," Farrell said in March 2013. "They hustled every play, turn down the baseline every chance at the plate. Everything they had was all out. We've seen that from Jackie. Both had good defensive capabilities. Jackie's got a better throwing arm. The one thing that came late with Grady was his power. He didn't hit for much power in the Minor Leagues, but that blossomed later on."
Sizemore, a left-handed hitter and thrower, didn't dispute that his history with Farrell might have factored into signing with Boston.
"I got a feel for him and I was around him quite a bit," said Sizemore. "I just kind of came up in that system along his guidelines, and it was one of those things where I had a familiarity with the manager, and he had seen me play and he knew what I was about. He knew kind of what to expect coming in for me. It made it a lot easier for my decision."
Farrell looks forward to renewing their relationship.
"We understand who he is as a person," Farrell said. "He fits what we value in a player in terms of he's strong, he's tough, he's got character."
The Reds were another team very interested in Sizemore. Why did he choose Boston?
"I thought medically they did a good job of laying out a good game plan for me and kind of giving me the confidence that when I do get here, there's a good plan in place to keep me on the field and keep me healthy," said Sizemore.
Before the injuries, Sizemore was one of baseball's premier outfielders, both offensively and defensively. He hit .290 while leading the league in runs and doubles in 2006, and he followed that with a pair of Gold Glove campaigns, in which his power numbers continued to increase.
In 892 games, Sizemore is a lifetime .269 hitter with a .357 on-base percentage and a .473 slugging percentage. In his four full seasons, he averaged 27 homers per year.
As hopeful as Sizemore is to get his career going again, he knows the true test won't come until Spring Training.
"I think I won't really know how I feel until I get out there and you're grinding every day," Sizemore said. "You can only do so much from a rehab standpoint or an offseason program. Baseball season starts, you're on your feet every day, it's long hours. When I get in that kind of format I guess, and see how I react when I'm pounding it every day week in and week out, that's kind of like the final test."