Wainright agreed to a two-way contract with the Suns on Monday, Shams Charania of The Athletic reports.
The Trail Blazers waived Wainright on Saturday.
Wainright played the final 1:56 of Tuesday's 130-113 win over the Kings, finishing with zero points (0-1 FG, 0-1 3Pt) and one rebound.
Wainright (knee) isn't listed on Portland's injury report for Saturday's game against Dallas.
Portland recalled Wainright (knee) from the G League's Rip City Remix on Friday.
The Trail Blazers assigned Wainright (knee) to the G League's Rip City Remix on Monday.
Wainright (knee) has been diagnosed with a left MCL sprain and will miss the next 4-6 weeks, Danny Marang of 1080 The Fan Portland reports.
Wainright is questionable for Friday's game against the Lakers due to left knee soreness.
Wainright was promoted to Portland's main roster Tuesday.
Wainright (calf) has been ruled out for Wednesday's game against the Pistons.