Manchester United have confirmed Radamel Falcao will return to AS Monaco following his season-long loan with the club.
Borussia Dortmund have made their first signing after Jurgen Klopp's departure by landing midfielder Gonzalo Castro.
On the back of relegation out of the Premier League, departures this summer would appear to be inevitable.
With release clauses having been written into the contracts of those snapped up in the hope of cementing a top flight standing, Cardiff could see their hand forced in the transfer market.
Club captain Hudson fears that may be the case, with Medel currently shining on the World Cup stage with Chile and Caulker having shown that he is capable of adding to his one senior cap for England.
Hudson told WalesOnline: “Obviously it’s well written that they’ve got release clauses in their contracts and they are both players that are highly sought-after.
“Gary has started well in the World Cup.
“If he goes on and has a really good World Cup, I can’t see why there wouldn’t be teams wanting him.”
The centre-half added: “I praise Steve Caulker all the time. He’s a success at the club for me.
“He’s a young British centre-half who’s only going to get better and a leader in his own right, so there’s going to be teams after him.”
A clause in Campbell’s contract has already been triggered by Leicester City and Hudson is not surprised to see a side heading for the Premier League looking at a proven marksman.
He said: “He’s another player with a trigger fee and a very small one for a player of his calibre and the way he performs and works hard.
“I’m sure there’ll be teams queuing up to take him. It will be tough to hold onto him for sure.”