Marshall-King limped off in the first half at Kogarah Oval on Sunday after his ankle was trapped in a legal Jack de Belin tackle.
The influential Dolphins No.9 was later spotted sporting a moonboot and could only watch on as his side slumped to a fourth loss in five games and fell to sixth spot.
The Dragons, meanwhile, have firmly entrenched themselves inside the NRL's top eight with a five tries to one victory that will give hope their wait for a return to finals football is growing closer.
NSW State of Origin star Zac Lomax was absent, while the Dragons also covered for the loss of Mat Feagai, who went off with a suspected shoulder injury as he went looking for the opening try of the afternoon.
It took until the 35th minute for either side to break through with Dragons No.6 Kyle Flanagan slotting a penalty from in front after Tevita Pangai Jr was pinged for a high shot.
The Dolphins, however, found a way to jag a 6-2 halftime lead as Jake Averillo sent in winger Tesi Niu, his try converted by Jamayne Isaako.
The Dragons began the second half with intent and were looking to exploit the Dolphins' frail edges.
The Dragons have proved too strong after the break for the Dolphins in Sydney. (Steven Markham/AAP PHOTOS)
Luciano Leilua had the ball stripped on the left edge as he tried to ground the ball before the Red V switched sides and Ben Hunt sent a rampaging Raymond Faitala-Mariner over the line.
The Dragons were in a mood for more and Flanagan was quickest to act when he snuck down the shortside off a scrum play and combined with Tyrell Sloan to send Christian Tuipulotu in on the left.
Sloan then weaved his way over before de Belin and hooker Jacob Liddle crashed in from close range to wrap up victory for the Dragons in the final quarter of an hour.
Arguably the biggest indicator of their improvement under coach Shane Flanagan came when the result was assured.
Dragons centre Moses Suli raced from the other flank to halt a runaway Herbie Farnworth from scoring by knocking the ball out of his hands with the tryline beckoning.