Upton, obtained from the Braves with closer Craig Kimbrel less than 24 hours before Opening Day, has been working out and rehabilitating his left foot.
Upton, the older brother of Padres left fielder Justin Upton, came down with sesamoiditis -- a painful foot condition -- in Spring Training with the Braves.
San Diego general manager A.J. Preller said Tuesday the reports on Upton's progress have been good.
"The reports we've been getting back are that he's able to run the bases and he's been able to swing the bat a little bit and get on the field," Preller said. "We will continue that here for the next week and re-evaluate it. That's kind of the next step.
"We're making sure every day that's he's not in pain and the foot is still healing."
That means a Minor League rehabilitation assignment is looming closer, which will give Preller and the front office a chance to lay eyes on Upton.
"I think that it's more about getting him healthy, getting him on the field and see where he's at," Preller said. "We will get a chance to see him in a rehab assignment and we'll be able to make a decision."
Upton comes to San Diego looking for -- counting on -- a fresh start after two tumultuous seasons with the Braves, during which he got a chance to play next to his brother, but struggled offensively, hitting .184 in 2013 and .208 last season.
Once Upton is healthy and ready to rejoin the big league team, the team will need to decide where he fits. There are four outfielders on the roster now, and Upton is owed $46.35 million on his contract.