There is Atletico Madrid and Arsenal that seem to have serious interests in the player with side talks going on.[...]Manchester United will try to bring back some wasted money for him since they bought him from Arsenal.
Are you sure about Arsenal? I haven't seen a reliable source confirming Arsenal's concrete interest in potentially signing Antony [I really hope it's just a rumor since he's not that effective in the EPL].- I believe in the latter part, you meant to type Ajax
but the big question is, will Saliba leave Arsenal. Arsenal are still very much in the UCL, and peradventure Arsenal wins the title, it will certainly affect Saliba's decision to stay at the club for a longer period, but if the reverse happens, then Real Madrid certainly have a chance.
No matter what happens in the UCL, I hope Saliba stays at Arsenal until the end of his contract [roughly two more years], but he hasn't been playing well lately [the number of silly mistakes makes me believe he has set his sights on a lucrative move to Real (I hope I'm wrong)].