Former Cambridge United player Darling signed a three-year deal when he joined Swansea from MK Dons in 2022.
He has started every league game alongside Cabango in Williams’ back four this season.
Cabango may be a doubt for Saturday’s game against West Bromwich Albion after coming off late in the Portsmouth defeat, while Nelson Abbey is no longer available after Williams confirmed that his season-long from Olympiakos has been brought to a premature end.
Abbey has left Swansea having made just one League Cup appearance since arriving in August.
“He has had a really tough time getting minutes here with the level of Harry and Ben, through no fault of his own,” Williams said.
“He is a terrific character and he will go and play brilliantly for somebody now. We thank him for all his hard work with us.”