Sir Alex Ferguson vows United will "not let Liverpool off" after opening an investigation into the Anfield club's conduct in the Gabriel Heinze affair.
The Merseysiders' drawn-out attempt to sign Heinze ended this week when a three-man Premier League arbitration panel ruled against the player's claim that a letter signed by United chief executive David Gill permitted him to sign for Liverpool.
"We are looking at Liverpool's whole role in this," said Sir Alex on Friday.
"We are not letting them off with it. That is what we are investigating."
Asked whether it was a case of 'tapping up' Heinze, Sir Alex responded: "David Gill is working on it at the moment. We will get to the bottom of it and see how it comes out."
Sir Alex insists he has no issue with Heinze, who eventually signed for Real Madrid.
"I've got no axe to grind with Gaby whatsoever. The issue without question is how much he listened to us rather than his agent. But his agent will make his few bob."
Sir Alex also responded to two points made by Liverpool boss Rafa Benitez. The latter lambasted the Premier League panel's decision but Sir Alex said, "There was never any chance of winning that case, so Rafa clearly did not read the Premier League rules."
Benitez also bemoaned Liverpool's share of early Saturday kick-offs.
"It is disappointing stuff," said Sir Alex. "He talks about the fixtures... he should have seen our fixtures over the last two or three seasons."