Vunivalu showed obvious discomfort in his left leg after a routine tackle in Saturday's 36-24 win over the Eels in the qualifying final at Suncorp Stadium.
But Storm trainer Matthew Barradeen ran onto the field as play continued and waved his arm to grab referee Ashley Klein's attention, well before he got to Vunivalu to assess him.
The Eels were on the attack up the other end of the field, but play was held up while the trainer stretched Vunivalu's limb.
Eels fullback Clint Gutherson and Storm forward Christian Welch can be heard having an animated disagreement over the hold-up.
The NRL rules around treatment of serious injuries state trainers cannot stop play "for tactical reasons".
Trainers can be barred for the rest of the game and clubs can face penalties ranging from a warning or a breach notice.
The Titans were fined $5000 earlier in the season for a breach involving a trainer stopping play during the match against Wests Tigers.
"So at this stage the Storm trainer has not even attended to Vunivalu; at this stage as no real idea of the extent of his injury," NRL head of football Graham Annesley said as he showed replays of the incident in his regular Monday briefing.
"Our rules are pretty clear when a game should be stopped for an injury. The treatment on the basis of it [the footage] appears to be for cramp. But I'm not going to make that assumption at this stage," he said.
"The rules are pretty clear though so we need to seek an explanation from Storm, which we will do.
"However on the base of it, it would appear a contravention of our rules. So we'll be in touch with Storm and decide if that matter goes any further."
Annesley said referees had come in for criticism of these types of stoppages.
But he reminded everyone of the April 2019 Cowboys match, when referees Grant Atkins and Gavin Badger allowed the game to continue while winger Nene Macdonald had a broken ankle.
"The referees were both dropped as a result of that. So whenever a trainer tries to stop a game the referees will respond to that."
The NRL's Operations Manual rule 9.1.1 states: "Any trainer who attempts to unnecessarily stop play for tactical reasons will not only be liable to Penalty under the provisions of the NRL rules, but may also be ordered from the playing area for the remainder of the Match."
In an unrelated point, Annesley also congratulated Klein on that match as it was the whistle blower's 300th NRL game in charge.
That is on top of the games of Super League Klein controlled before returning to the NRL in 2009.