The brothers entered their pleas at the Maricopa County Superior Court on Thursday.
The Morris twins were charged for helping three other men attack 36-year-old Erik Hood at the Nina Mason Pulliam Recreation Center in Phoenix on January 24.
According to Hood, who used to mentor Marcus and Markieff when they were in college, he was confronted by one of the men before being struck in the back of the head by another.
Upon trying to run to his car, Hood collapsed and was subjected to a vicious assault, which he claims the Morris twins took part in, and was left with a fractured nose, abrasions and a large bump on his head.
The Suns refused to comment on the situation or about whether both players would be released from their contracts.
The twins signed four-year extensions last summer, with Markieff bagging 32 million dollars and Marcus receiving 20 million.
Markieff and Marcus, both of whom are 6-foot-9, will appear in court once more on June 30.