Everton have called for Chelsea boss Jose Mourinho to retract his comments about striker Andrew Johnson.
Mourinho branded the England striker "untrustworthy" following a challenge with Chelsea keeper Hilario on Sunday.
An Everton statement said: "To query a player of Andrew's integrity is wholly unacceptable and possibly defamatory."
Everton are thought to have taken legal advice over the matter and the statement added: "We ask Mr Mourinho to immediately retract his allegations."
The joint statement from Everton and Johnson's agent Anthony McFarlane, also called on the Football Association to look at Mourinho's comments.
It said: "We would urge the footballing authorities to look closely at Mr Mourinho's comment and then, perhaps, seek a formal explanation.
"Both Everton FC and Andrew Johnson have always believed in the virtues of fair play."
"Jose Mourinho has no right to say things like that"
Johnson's tumble in the box under Chelsea keeper Hilario's challenge sparked a touchline row between Mourinho and Everton counterpart David Moyes after the Chelsea boss made a diving motion with his hands.
Mourinho said: "He's dangerous for opponents because you cannot trust him, and I was not happy with that.
"But I think he was a bit embarrassed and he behaved very well after that."
The Chelsea boss stopped short of calling Johnson a cheat, but said: "In my country we call them 'intelligent' players. In other countries you can use different words and are critical.
"I've been in this country for three years now and I am influenced by your culture. It is a country I admire, I am proud to be part of it.
"For me when a player chases a penalty, he is no longer an intelligent player."
Everton midfielder Phil Neville was incensed by Mourinho's comments, which came weeks after Arsenal boss Arsene Wenger said Johnson went down too easily in the box.
606: DEBATE
"Jose Mourinho has no right to say things like that," said Neville. "It wasn't a case of cheating at all.
"The reason why Andrew Johnson is not getting penalties at the moment is because people like Arsene Wenger and Jose Mourinho are coming out and having a go at our players.
"It is nothing to do with him. He should leave everything that is concerned to Everton FC to our manager and our chairman."
And Everton boss Moyes dismissed Mourinho's insinuations of Johnson's diving and accused him of hypocrisy.
"After all, he's got a big 15 stone striker up front who is quite partial to it himself.
"I saw the incident on television and I don't think it was a penalty, but it certainly wasn't a dive either.
"A few weeks ago the Chelsea keeper got caught by a Reading player who was criticised for that.
"Our player is slightly bumped, straddles the goalkeeper and jumps over him. He's missed the keeper and he gets criticised for that, so you can't win."
A Football Association spokesman said: "We are aware of what's been said but have no comment to make at this stage."