Kevin Durant's Achilles injury has the Warriors superstar down in the dumps ... so says his own mom, Wanda, who says, "He's having a rough time right now."
KD fought like to hell to return from a calf injury he suffered last month to play in Game 5 against the Raptors on Monday ... but he appeared to pop his Achilles just a few minutes into the 2nd quarter.
Wanda says the whole ordeal has taken a toll on her son ... saying on "Good Morning America" on Wednesday that KD ain't doing so well after the injury.
"Emotionally, it's a little tough for him," Wanda says ... "He's having a rough time right now."
"He just told me not to cry. ... He just told me he was going to be okay and don't worry."