SAN ANTONIO — San Antonio Spurs forward Tobias Harris will miss the preseason and is questionable for the start of the regular season after suffering a strained left calf during training camp. Harris, who signed as a free agent on July 6, did not participate in the team’s annual intrasquad Silver & Black scrimmage on Sunday. The 6-foot-8 power forward will be reevaluated following the team’s five-game preseason schedule. Team officials said Harris is questionable for the regular-season opener against Oklahoma City on Oct. 20 in a rematch of last season’s Western Conference Finals. Harris signed a two-year contract with San Antonio after spending the past two seasons with Detroit. He averaged 13.3 points, 5.1 rebounds and 2.5 assists in 27.7 minutes last season to help the Pistons finish atop the Eastern Conference standings.