Despite the 29-year-old's status at Molineux, Castles says that Wolves are prepared to negotiate a deal if any club shows a willingness to meet their £70m valuation.
Speaking on the Transfer Window Podcast, Castles said: "I think Wolves have been quite open about this with Jimenez for some time now. They are ready to let the player leave in their transfer demands can be satisfied.
"He can go to a bigger club as he has established himself as one of the top Premier League strikers. He has done extremely well in European competitions and is 29 years of age.
"If Manchester United or Juventus, who are pushing far harder for the player at present, come up with the right offer they will sell him and allow him to move on."
Jimenez, who still has three years left on his contract, has scored 43 goals from 97 appearances for Wolves in all competitions.