Tucson TV station KOLD reports the suit was filed Thursday in Pima County Superior Court by former Georgia Tech booster Ron Bell and his girlfriend, Jennifer Pendley.
Last month, Pastner filed a defamation lawsuit against Bell and Pendley, saying the Oro Valley couple was trying to defame and blackmail him by accusing him of breaking NCAA rules.
The countersuit claims Pastner sexually assaulted Pendley in February 2016 when he was head coach at Memphis.
In a statement, Pastner's attorney Scott Tompsett called the latest suit "false and malicious" and says his client never acted improperly with Pendley.
Pastner said after Tech's 77-54 loss at Louisville Thursday night that he was "an absolute victim in this whole deal."
The coach added, "It's unfortunate, but I'll deal with it. All my wife and I try to do is be compassionate to people and that's life, so you live and learn.
"But unequivocally, zero, zero, zero, zero, zero, zero truth to any of those disgusting, bogus allegations. It's disgusting," before saying "zero" 11 more times.
Pastner played at Arizona from 1996-2000 and was a Wildcats assistant coach from 2002-08 before being hired by Memphis in 2009.
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