The Force, which narrowly missed this season's grand final, is a founding member of the NSL in 1977 and has won three championships.
But Force president Bob D'Ottavi has stated that the club was losing A$1.5million a year from fielding its NSL side and could not afford to continue doing so.
D'Ottavi, who has helped fund the club from his own pocket, said he told a meeting of members on Sunday that unless a new financial backer came forward by June 22, the club would pull out of the NSL.
It would continue as a club in Adelaide's Premier League competition.
D'Ottavi admitted it was unlikely such a sponsor would come forward as there had been no interest shown at all so far.
He said: "Unless some fanatical people want to invest the money in the national league team, we don't want to put the club in jeopardy.
"It's not that the club can't survive, we have got enough money to go on next year, but Adelaide City definitely won't be in the National Soccer League unless we have got backers coming in."
D'Ottavi said he expected little help from Soccer Australia (SA) given it was embroiled in its own problems over the make-up of its board.
"There's not much option if you know the state of the board of Soccer Australia. The board is probably not going to help the club anyway."
Adelaide City Force is the latest Australian soccer franchise to hit financial trouble with the club set to pull out of the National Soccer League (NSL) unless a white knight investor can be found.
