It's a big "if", but if Marshall was to be ruled out for any length of time, Black would be thrust into the firing line to start this Saturday's bumper clash against the Chiefs at Westpac Stadium in the capital.
Hurricanes coach Chris Boyd would also need to search the country to find a player to sit on the bench behind Black, given there are few other pivot options in his squad. Outside back Jason Woodward could play No10 at a pinch but he broke his ankle playing club rugby recently.
"Boydy will find another one. He'll have to," Plumtree said.
The results of Marshall's scans are likely to be known today. Nehe Milner-Skudder suffered a head knock on Saturday but Plumtree said he had no further information on how the fullback had progressed.
The Hurricanes will field a full-strength side against the Chiefs this week as they look to extend their lead at the top of the Super Rugby standings. The Chiefs are second in the New Zealand conference.
"They're 10 points behind us and they'll need to win this to keep in touch with us so we are aware of that," Plumtree said.
The Hurricanes will finish their campaign with five Kiwi derbies, including two meetings with the Chiefs, and four of their All Blacks - Conrad Smith, Ma'a Nonu, Cory Jane and Ben Franks - still need to rest one more game each.