The former Milan, Real Madrid and England manager, speaking to La Gazzetta dello Sport, addressed the Rossoneri's decision to turn to Amorim following the departure of Massimiliano Allegri.
"Amorim at Milan? It's a double leap into the unknown, both for him and for the Rossoneri," Capello said.
Amorim is expected to sign a contract running until 2028, with the possibility of a further year's extension, formally ending his six-month absence from football management since leaving Manchester United in January.
Capello expressed frustration with the lack of clarity that surrounded the search for Allegri's successor.
"I've heard so many names, all different from each other. Nationality, style of play, ideas. I think it's the manifesto of the confusion hanging over Milan."
He added some nuance to his criticism, acknowledging Amorim's earlier achievements before his troubled spell in England.
"The Amorim I saw in Lisbon had convinced me, of course you also have to consider the work done in Manchester. I don't know, it all seems a bit left to chance."
Capello's comments come after AC Milan finished outside the Champions League qualification places last season, a result that prompted the club's hierarchy to part ways with Allegri and several senior figures, including sporting director Igli Tare.
Discussing the contrasting nature of Amorim's two most recent jobs, at Sporting Lisbon and then Manchester United, the 79-year-old offered some pointed advice.
"They will have to explain to him that Milan is a club with a history to honour and respect. And that results worthy of that history need to be delivered."
Capello did not shy away from highlighting where Amorim fell short during his time in England.
"He didn't manage to get into the players' heads at United. At Milan he will have to succeed."
He also pointed to the importance of the players Amorim will have at his disposal in determining whether the move proves successful.
"Then, the players he has available will also make the difference. I can say it's a leap into the unknown for both. The Rossoneri are bringing in a coach who doesn't know the league, and he... has to redeem himself after a failed experience."
Amorim's win percentage at Manchester United stood at 38.1 per cent across all competitions, a figure inflated by a run to the Europa League final, with his Premier League record sitting at a more modest 31.9 per cent.
Milan's decision to appoint him reflects a willingness to take a chance on a coach whose tactical identity, built around a back three, represents at least some continuity from Allegri's own system in his final season.
Whether Capello's scepticism proves justified will likely become clear quickly, with Milan facing immediate pressure to return to the Champions League after two consecutive seasons on the outside looking in.