PHILADELPHIA -- Phillies ace Zack Wheeler will not make his scheduled start on Sunday against the A's because of left lower back tightness.

The club expects Wheeler to rejoin the rotation following the All-Star break.

¡°We¡¯re going to be cautious,¡± manager Rob Thomson said.

Wheeler left Tuesday¡¯s 10-1 win over the Dodgers after the fifth inning because of back tightness, which Thomson later called back spasms. Wheeler said his back had been bothering him for at least a couple of starts.

Nobody seemed particularly concerned on Tuesday, but Wheeler underwent an MRI on Wednesday. It revealed no structural damage, according to Thomson.

Thomson said the Phillies are confident the extra rest will rid Wheeler of his back issue. Philadelphia has not set its rotation coming out of the break. Hypothetically, Wheeler could pitch as early as July 19 in Pittsburgh (the Phillies¡¯ first game after the break) or as late as July 23 in Minnesota (their fifth game after the break).

Thomson added that he isn¡¯t sure yet who will pitch on Sunday. If the Phillies don¡¯t use many relievers on Friday and Saturday, Thomson could use them in a bullpen game on Sunday. But if they use their bullpen enough on Friday and Saturday, the club might call up somebody from Triple-A Lehigh Valley.

Meanwhile, Bryce Harper, who did not play Wednesday because of a bruised left hand, returned to the lineup on Thursday.