"You have to be concerned now," MacPhail said. "To me, you get 10 games into Spring Training before you really start paying attention, but the clock is starting to be an issue.
"It's getting to be something that's on my radar screen, even though at the present time our athletic staff feels like he's going to be ready by Opening Day. By now we have to start thinking about, 'What if he isn't ready?'"
When asked if the team would seek outside relief to temporarily fill the hole at second base, MacPhail didn't rule out the option.
"We will see what's out there," he said. "Obviously, we have weekly calls with our pro scouts, and we have to let them know what's going on in our camp. We might have to shift their focus a little bit from what the initial menu was. And then, obviously, we are going to have to start exploring more internal options as well."
Roberts' progression in rehabbing a slight herniated disc in his back hit a speed bump on Monday night, after medication he was prescribed on Sunday upset his stomach.
Orioles manager Dave Trembley said Roberts was prescribed a megadose pack, which is similar to a cortisone shot, to help reduce the inflammation and is now suffering from symptoms generally caused by a stomach virus.
Roberts was confined to the team's training room on Tuesday and the initial course of action is to stay away from baseball-related activities for three days.
"He'll be rechecked on Thursday," Trembley said. "And we're confident that's when he'll start baseball activities again."
The 32-year-old Roberts began experiencing nagging back spasms during his offseason workouts at the Athletes' Performance Institute in Arizona and was originally misdiagnosed with kidney stones before doctors found the herniated disc a week later.
Prior to the illness, Roberts had been progressing nicely from his injury. The former All-Star hadn't seen any game action, but was a full-go in the Orioles practices, even taking full-fledged swings in batting practice.
"You saw him out here. He's doing everything. He's taking ground balls, turning double plays, taking BP," Trembley said. "But there was still some inflammation there, so they thought maybe take this medication orally, that would alleviate it. So he took it."
Trembley said Roberts didn't take the medication because of a setback, and was still optimistic that the team would be able to get their starting second baseman on track this spring.
Both Trembley and hitting coach Terry Crowley believe a regular position player like Roberts needs 25-30 at-bats to be ready for the season.
"I'm still confident we can get him that," Trembley said. "But I'd still like to see him on the field."
Robert Andino would figure to be the leading candidate to fill in for Roberts. Trembley has said earlier this spring that Andino is the team's back up middle infielder. Still, Andino has struggled this spring, going 1-for-11 in four games. Other middle infielders in camp include Justin Turner, Miguel Abreu and Michael Aubrey.
Brittany Ghiroli is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.