Nethercott, who has one year left on his current contract, fears he will not be offered a new deal after club chairman Theo Paphitis hinted that his place was under threat.
As a result, the 30-year-old defender says he is ready to listen to other offers, with Gillingham and Queen's Park Rangers thought to be leading the chase.
"I seem to have been written off already before a ball has even been kicked," Nethercott told the South London Press. "That is very disappointing.
"I definitely want to be involved in the squad but I have to look after my future. I have got a five-year-old son and a family and I need to look after their interests as well as mine.
"I am not guaranteed a new contract - so I have no alternative. "