Hysen, the first former player to speak out about Keane's 27-month spell, said he was moody and unapproachable.
Hysen, 26, said: "Because of Keane's reputation people were afraid of trying to talk to him. He wanted players to speak but they didn't.
"It was OK for me at first as I was in the team but any of the lads who were cut out had no relationship with him.
"At times he was very harsh. He would have a go at players, tell them that they were worth nothing."
Sweden midfielder Hysen was axed for a cup trip to Barnsley for turning up late for the bus and was later dumped by Keane following a solid start on Wearside.
He signed from Djurgarden for £1.7million in 2006 but went back to Sweden to join IFK Gothenburg a year later.