Kaizer Chiefs have reportedly shown interest in the player, who has struggled for form this past season due to injury among other things.
Castro has played second fiddle to the likes of Percy Tau, who stole the show last season as Downs narrowly missed out on the PSL title to Bidvest Wits.
He made 22 appearances in all competitions, scoring only one goal, a stark contrast from his debut spell where he found the back of the net 10 times in 23 outings.
Castro has an offer to extent his deal until 2020, but according to his agent Joao Bentancourt the club has decided to delay offering him a new deal as they look to see whether he will be able to revive his form.
The striker will be free to negotiate and sign a pre-contract with any team of his choice as of January next year as he will be in the final six months of his existing Sundowns contract.
This has reportedly opened up the door to the Amakhosi, who are keen to beef up their striking department
Chiefs reportedly see Castro as their preferred man to lead their attack in the future.
All in all, it remains to be seen what the future holds for the 28-year-old forward.