They may also have to convince players who've hardly been used this year, such as Siphelele Ntshangase and Joseph Molangoane, to stay on as their contracts expire in June.
Chiefs confirmed they would appeal to the Court for Arbitration in Sport (CAS), after Fifa - in a 15-page ruling seen by Sowetan - found they had "induced" Dax to terminate his contract with Fosa "without just cause" in June 2018.
Dax, now on loan at Black Leopards, contended he was under no contract with Fosa and declared himself a free agent. Fosa demanded compensation but Chiefs offered $25,000, which the Malagasy club turned down. They told Fifa they wanted ?150,000.
Fifa's players committee eventually ruled Dax could register with Chiefs, but Fosa took the matter further, leading to Chiefs and the player now compelled to compensate the club to the tune of just over R600,000. Dax and Chiefs must share the costs equally, according to the ruling.
Dax, 28, earned as little as R6,000 per month at Fosa before he signed for Chiefs two years ago. Chiefs hiked his salary to R60,000 per month and it would have increased to R70,000 by July this year. He was also set to get R960,000 in image rights over the three-year period ending July 31 2020.
Fifa found his contract with Fosa to be valid, despite protestations from Chiefs and the player that his signature may have been forged.
The parties must file their appeals by February 28, or compensate Fosa by March 7.