Castagne came close to joining Celtic for £8m in the last transfer window but the deal collapsed when the Italian outfit increased their demands to £12m.
They now want around £20m from The Eagles knowing that they can attach a large premium when a Premier League club want a player.
Castagne favours a switch to the Premier League even though he helped Atalanta qualify for the Champions League.
A lot has been made of United’s move for Wan-Bissaka, with Eagles legend John Solako claiming the defender should stay in south London.
“He couldn’t have been lying in bed and dreamed of a better debut season. He probably needs more games,” Solako said.
“I would compare him to Nathaniel Clyne who came through the system at Palace and was tremendous.
“He played 120-odd games and then went to Southampton, Liverpool, played for England and everything seemed to fall into place for him because he had that maturity.
“He knew his job and he was confident in himself and his game. It’s too early for Aaron. He needs another season.
“I’m not surprised Manchester United have come in because they could probably get him cheaper and they think they need to do something now.
“You remember with Walcott and those types of players who came through at Southampton – even [Gareth] Bale or [Alex] Oxlade-Chamberlain – they came early and it took them years to find their feet.
“I don’t know why teams don’t buy them and then leave them with their club and loan them back for a season or two, just to get that maturity.”
