United had been due to face Edinburgh United on Saturday but admit that a shortage of bodies, for a variety of reasons, has left them unable to compete.
The club announced the news on Friday evening at the same time it confirmed former Brechin City striker King had left his role.
A club statement said: “Our squad has been stretched beyond the limit with injuries, illness and isolation, whilst attempts to register new players were not completed in time.
"Further illness behind the scenes has also impacted upon club operations recently and we wish those involved a speedy recovery.
"Please note that the manager's decision to step down has not had an impact on this situation.
"We therefore apologise for any inconvenience caused to those involved tomorrow, particularly to our hosts.”
On King, Saints added that it had been “with regret” that the two had gone their separate ways.
"Charlie has been considering his position for a few weeks and decided to offer his resignation yesterday, which was received with a heavy heart,” the club said.
"There is no question that Charlie has worked incredibly hard throughout the last 18 months as boss and it is most unfortunate that results on the park have not reflected that commitment.
"Indeed, the pressure of the Covid-19 pandemic has placed a huge strain on the football club as well as the coaches and players.
"As a result, the manager was working under the constraints of reduced income, training in bubbles, league campaigns declared void, showers and changing rooms roped off, the imposition of travel restrictions and players isolating at short notice.
"The current injury situation and a struggle to find replacements has also taken a toll on the squad but Charlie's decision was not taken lightly.
"Assistant manager Drew Fleming will also be leaving this weekend and the club would like to wish both men all the very best for the future.”