Sizemore has passed all tests so far, but there are a few more before the team can declare him the starting center fielder for Opening Day.
"We'll probably have a better read on that in another 10 days," manager John Farrell said. "Because next week, we're hopeful to have him play five times. There's been a pretty well thought-out plan to the increase in volume. We're going to take every available day to gather as much information."
Farrell projects that, following an off-day Friday, Sizemore will play three days in a row for the first time from Saturday to Monday.
"I didn't know how the body was going to hold up day to day, if I was going to be able to push it every day," Sizemore said. "So far it's allowed me to keep upping the volume and pushing the intensity. I still don't feel like I've reached that ceiling where I went too far. As long as I'm there, I'm happy."
The one thing Sizemore has not yet done is steal a base.
"We've put him in motion a couple of times already," Farrell said. "But to say we're just absolutely going to turn him loose with the green light ... we'll try to continue to ramp up his volume before we look to do anything situationally that might be different than what we've gone through right now."
There will come a time when the brakes come off completely.
"At a point in time in hopefully the near future, that all becomes 'react to the game,' and we've seen every other phase of his game be natural and second nature to him," Farrell said. "He's advanced on a ball in the dirt; we've put him in motion two or three times. There's no hesitation on him sliding or anything like that. So far, so good."
Sizemore is hoping his skills will continue to come back to him as the days evolve.
"Everything feels good, but I still feel like there's a lot of room for improvement -- getting breaks, getting a better first step, feeling more explosive, feeling that quickness in that good first step," Sizemore said. "I'm happy with where it's at, but I'd like a little bit more improvement."
Ian Browne is a reporter for MLB.com. Read his blog, Brownie Points, and follow him on Twitter @IanMBrowne. This story was not subject to the approval of Major League Baseball or its clubs.