The San Antonio Spurs may have to miss the services of forward Tim Duncan for some time, with head coach Gregg Popovich not providing a timetable for the return of the veteran big man from a sore right knee. 

Popovich said Duncan will have a "regimen of rest and rehabilitation" after having a magnetic resonance imaging (MRI) on the knee Wednesday, ESPN reported. 

Duncan already missed three of San Antonio's past four games because of the nagging injury. 

A 117–89 win over the Phoenix Suns on Thursday last week was the first game Duncan missed due to the knee. 

However, he played in the game against the Los Angeles Lakers the day after, tallying four points, three rebounds, three assists, one steal, and one block to help the Spurs win 108–95. 

Unfortunately, the knee kept him out in their last two games, first a 120–90 loss to the Golden State Warriors Monday, and a 130–99 bounce back victory over the Houston Rockets Wednesday. 

In the 39-year-old's absence, Popovich used two different starters in his place, veteran David West had the starting job against the Suns and Warriors, while second-year forward Kyle Anderson started versus the Rockets. 

It is likely that Popovich will be switching the two in the starting lineup if Duncan continues to sit out in games.  

Up next for the Spurs will be a road trip to the Quicken Loans Arena this Saturday to take on a familiar rival in LeBron James, who is leading the best team in the Eastern Conference, the Cleveland Cavaliers (32–12). 

Duncan's status for the game against Cleveland remains uncertain, but if he is good to go by Saturday, there is no doubt Popovich will let him play. 

Currently, the Spurs are second in the Western Conference and in the league at 39–7, just three games behind the reigning champions the Warriors, who just recorded the best start in 46 games with a 42–4 record.