The admission comes in the Manchester United midfielder's forthcoming autobiography, which is being serialised in two British newspapers.
The Irishman says he "had waited long enough" to exact revenge on Haaland after suffering a knee injury while playing against the Norwegian in 1997.
Haaland was left with damaged knee ligaments after being fouled in the Manchester derby of April 2001 and has not started a game since.
Keane's book also reveals he added insult to injury by taunting Haaland while he lay stricken on the ground.
"And don't ever stand over me again sneering about fake injuries, and tell your pal (David) Wetherall there's some for him as well," Keane is quoted as saying.
Keane was sent off for the tackle - and in the book he claims: "I (didn't) wait for Mr Elleray to show the red card. I turned and walked to the dressing room."
An FA statement said: "These comments have been used in newspaper serialisations of Roy Keane's forthcoming autobiography.
"Having read the comments we would like to see the book in its full context before making any decision.
"However we clearly would never expect any one individual to set out to physically hurt an opponent at any level of the game."
The suggestion of a premeditated attack has also alerted Haaland, who has hinted he may take legal action against Keane.
The 29-year-old was quoted on Tuesday in British newspapers as saying: "Am I going to sue? Make your own mind up. I've played only a few games after the tackle.
"I will go in and see if I can find any of Keane's studs inside there."