ADELAIDE is believed to have guaranteed Kurt Tippett $200,000 outside of his contract and suggested the arrangement be kept secret from the league.

The AFL is investigating correspondence between the Crows and Tippett's management that refers to a list of companies that could provide the additional payments, not acknowledged in the three-year contract the forward signed in 2009.

The letter sent from former Crows football manager John Reid to Tippett's manager Peter Blucher is also understood to provide a guarantee the Crows would cover the money - split over two years - if it was not sourced via the third parties.

Tippett's immediate future was in limbo last night, with a trade to Sydney or any other club unlikely to be approved ahead of the conclusion of the three-week trade period at 2pm today.