The NBA's winningest team is also without veteran Antonio McDyess, out with a sore back, and it all comes with nine games left in a season that has seen the Spurs coast in near-perfect health.
All four starters were out for Monday night's game against Portland.
The Spurs hosted the Trail Blazers on a three-game skid, their longest all season. Richard Jefferson was the only starter left in the lineup.
In the case of McDyess, at least, Spurs coach Gregg Popovich was being cautious with the playoffs imminent.
"Money time is approaching," Popovich said.
San Antonio's next game is Thursday against Boston. Popovich hinted that Parker (left knee contusion) could return by then, but said the timetable for Ginobili (left quad contusion) and Duncan remains unknown.
Duncan has been out since spraining his left ankle last week in a victory over Golden State. He didn't travel with the Spurs on their three-game road trip to Denver, Portland and Memphis.
San Antonio left each city with a loss. It's just the third time the Spurs (57-16) have lost consecutive games during what has so far been the best regular season in franchise history.
Ginobili (17.8 points per game), Parker (17.5), and Duncan (13.1) are San Antonio's three leading scorers.
The Spurs began Monday night with a four-game lead over the Los Angeles Lakers for first place in the Western Conference. San Antonio has kept a healthy lead for the No. 1 seed most of the season, but the surging Lakers already moved three games closer in the past week.