The investigation centres on whether the Crows entered into a secret agreement that would allow Tippett to return to Queensland or move to a club of his choice at the end of his three-year contract.
"The Australian Football League wishes to advise it has recently become aware of a matter regarding the contracting of player Kurt Tippett to the Adelaide Crows in 2009, to cover the 2010-2012 AFL seasons," the league said in a statement on Wednesday.
"The AFL is still in the process of investigating this matter and how it relates to the operation of the AFL Player Rules.
"The AFL has no further update to provide at this time."
Relations between Adelaide and Tippett have soured since the player confirmed he wanted to be traded to Sydney rather than join Brisbane Lions or Gold Coast.
Fairfax Media reports on Wednesday said Crows chief executive Steven Trigg had met with the AFL last week to confirm they had agreed to trade Tippett for a second-round draft pick - a promise not disclosed in the deal submitted to the league.
If found guilty under AFL rules, Tippett could be suspended from playing for agreeing to such an understanding, while the Crows face draft penalties for up to four years.
Meanwhile, midfielder Koby Stevens has joined Western Bulldogs from West Coast, two days before the end of the trade period.The Bulldogs handed over pick 44 in the national draft to the Eagles, while the clubs also swapped later picks.