Speaking on his Rest Is Football podcast with Gary Lineker and Toon legend Alan Shearer, Richards said the statement issued by Isak on Tuesday night had made him change his mind on the striker's behaviour.
"I've defended him," Richards said.
"I've been on all the broadcasters saying 'I don't think it's fair to have an opinion when you don’t know what’s happening’ but now he’s spoken and those were his words, I feel like now he’s disrespected the club."
Isak's statement said that he 'lost trust' with the club and that change was 'in the best interests for everyone'.
Isak said he had lost trust in the club.Isak said he had lost trust in the club. (Image: Steve Welsh/PA Wire) "I don’t think its fair to himself, to his teammates, and to the fans," Richards said.
"I didn’t want to jump to conclusions because I didn’t think it was fair, but now, I feel he’s crossed the line."
It comes after Shearer said the situation was an “absolute mess” as he blasted the Swede's agent Vlado Lemic, in a conversation with Betfair.
“If I was him, I’d get his agent in a room and sack him on the spot immediately, because he is meant to be giving him the advice to sign that six-year deal and there’s no get out clause,” Shearer said.
Richards said he would even look at selling Isak for a little bit less than the asking price.
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"I just find the whole situation sad, but it’s intriguing too because there has to be a conclusion.
"I would, if I was Newcastle, take a little bit less [for Isak’s fee]. Because if he stays there and his head’s not right, then his value is only going to go down."
Newcastle play Isak-suitors Liverpool on Bank Holiday Monday, in a game under the lights at St James' Park, kicking off at 8pm.