Roberts hoped to play an extended spring training game last week, but his debut was pushed back by pain in his back. His condition has not improved.
"He's going to go through some additional testing. We really don't know to what extent, if any, but he is going to have some additional tests run," Andy MacPhail, the Orioles director of baseball operations, said Tuesday.
Orioles interim manager Juan Samuel called the news "not very good."
Roberts missed much of spring training after receiving an epidural shot for his back. He played his first exhibition game on March 26 and then participated in the first four games of the regular season before hurting himself while stealing second base in a game against the Toronto Blue Jays on April 9.
Roberts has been on the disabled list since mid-April. The two-time All-Star has thus far avoided having surgery on a herniated disk, a procedure that would probably force him to miss the remainder of the season.
Roberts' initial bid to participate in extended spring training was interrupted by pneumonia.
"There have been a couple of times where he really started his baseball activities and then pneumonia popped him back," MacPhail said. "We've gotten close to that start-up date, but we can't seem to get over the hump. We'll just see. Rather than being concerned, we'll wait for the information and then act from there."
The Orioles have used seven different players in the leadoff spot in place of Roberts, who last year was voted the team MVP and set new career highs in doubles (56), runs (110) and RBIs (79).