Dr. Preston Phillips -- a former WNBA team doctor -- was the main target in the deadly mass shooting at a hospital in Oklahoma this week that left four innocent people dead.
A male gunman opened fire on the second floor of the Warren Clinic in Tulsa Wednesday afternoon ... after police say a patient of the hospital traveled to the clinic with multiple weapons and opened fire.
Cops say the killer -- who we've chosen not to identify -- was furious with Dr. Phillips after the orthopedic surgeon recently operated on him, claiming the procedure caused him terrible back pain.
Officials say the man went to a local gun store on Wednesday -- just hours before the shooting -- and bought a semi-automatic rifle which he eventually used in the attack.
Phillips, aside from being a highly respected doctor in the city, also served as head team physician for the Tulsa Shock ... beginning in 2010.
The Shock moved to Dallas in 2016 ... where they currently play.
Indiana Fever assistant coach Gary Kloppenburg, who coached for the Shock from 2012-2013, penned an emotional letter to Phillips on social media, and blamed Oklahoma Governor Kevin Stitt for weak gun laws.
"Lord help us, our wonderful WNBA Tulsa Shock team doctor Preston Phillips was one of the innocent people murdered in the latest mass shooting."
"Such a kind and compassionate man who loved basketball and looked out for our players."
"The dereliction of duty by the OK legislature and Governor Stitt who have failed to protect their citizenry by implementing insanely loose gun laws hits close to home. RIP Doc"