Cumberland, 23, had been at the Padres' Spring Training facility in Peoria for 15 days taking part in the organization's annual minicamp for some of the top prospects.
"He looked great," Smith said of the initial reports on Cumberland. "I worried the last few days because he seemed frustrated. Maybe that's because some of that [symptoms] were creeping back a little."
Cumberland was diagnosed last summer as having bilateral vestibulopathy, which means the portions of both inner ears that control balance are damaged. That diagnosis followed months of visiting specialist after specialist to find out what was troubling him.
Cumberland's condition, coupled with a history of concussions as an amateur then later a professional, explained why he had debilitating migraine headaches as well as vision and balance problems his entire life -- including, at times, during games in the Minor Leagues.
Cumberland had impressed the front office staff with his play very early in minicamp, especially since he didn't play at all last season.
"I just think it was the daily physical demands of being a professional baseball player," said Smith, who noted that Cumberland didn't suffer any blows to the head in minicamp. "He worked out really hard [in the offseason] and didn't have problems. But there's a big difference between working out and playing the sport."
Cumberland was unavailable for comment on Monday.
Cumberland effectively retired on June 24 and later joined the coaching staff at Class A Fort Wayne -- reluctant to believe that his promising career was over.
He didn't stay retired long, though.
In early November, Cumberland was referred to the Sports Concussion Institute in Los Angeles, where he underwent a round of testing. He got the good news a few days later that he could resume playing, though while wearing a protective mouth guard to guard against future concussions.
Cumberland was taking a medication called "Brain Armor" and was doing eye exercises on a computer to improve brain health and its performance.
Cumberland, who Baseball America rated as the Padres' ninth-best prospect a year ago, came to Peoria optimistic that he would be able to resume his professional career after a quiet winter when symptoms that bothered him in the past were essentially nonexistent.
"I couldn't be more excited. Especially when I got the news in November it's a second chance. Not too many people get a second chance at something they love to do," Cumberland said in February. "I feel like I'm going to take it and run with it, and hope for the best and work hard every day."
San Diego outfielder Blake Tekotte, a good friend of Cumberland's from their days in the Minor Leagues, said the news of Cumberland's retirement was "heartbreaking."
"He's been dealing with it for so long ... it's such a tough situation for him," Tekotte said. "But you never knew when it was going to pop up. And he's never one to make excuses why he can't play. He worked so hard for this."
That was the toughest thing for Smith, knowing how talented Cumberland is when healthy and what a bright future he seemingly had ahead of him.
"It absolutely breaks your heart ... he's part of our family," Smith said.