Chief executive Mark Arthur and director of recruitment Keith Burt have been axed by club chairman Fawaz Al Hasawi, a member of the Al Hasawi family that owns Forest.
And the exit of former boss Clark is likely to shock supporters given his lengthy association with the Championship club.
Asked about rumours of his sacking, Clark said: "I don't want to say any more about it, for obvious reasons, but that is true.
"It's a shock, it's certainly a shock. Right out of the blue - a real shock."
It has been a period of upheaval at the City Ground and things show no signs of settling down following the latest developments.
The Al Hasawi family completed their takeover of Forest in the summer, appointing Sean O'Driscoll as manager.
But O'Driscoll was surprisingly replaced by Alex McLeish last month, with Arthur, Burt and Clark now following him through the exit door just three weeks later.