McGrady scored 13 points with nine assists on Sunday, as the Rockets clinched a playoff berth by beating the Los Angeles Clippers. McGrady took a painkilling injection on Tuesday and skipped Wednesday's shootaround.
Coach Rick Adelman wasn't sure if McGrady would play against Phoenix on Friday.
"I have no idea," Adelman said. "It's a day-to-day thing. Past tonight, I don't know. We'll have to wait and see tomorrow."
While McGrady sat out, point guard Rafer Alston returned Wednesday after missing three games with a strained left hamstring. The Rockets won the three games Alston missed, with Bobby Jackson starting and rookie Aaron Brooks coming off the bench.
The Rockets have five games remaining in the regular season and can still mathematically earn the No. 1 seed in the Western Conference playoffs.