Marshall also insisted his decision to rest Galvin for round 15 did not come as a result of reports the 18-year-old was disgruntled.
The Tigers coach anticipated the teenager would return to NRL action against Canberra on June 23, despite Galvin carrying a minor hand injury.
Galvin burst onto the scene with the back-to-back wooden-spooners early this season and was instrumental in wins over Cronulla and Parramatta in the opening month.
But amid the nine-game losing streak that followed, reports emerged that Galvin's management had approached Tigers powerbrokers to voice concerns over the club's direction.
Chief executive Shane Richardson has since met with the five-eighth's parents, with Marshall confident the Campbelltown product will remain at the Tigers beyond this year.
"(Galvin's parents) made it clear that he wants to stay and he wants to be here and he's with us, with our vision moving forward," Marshall said.
"That's all that needs to be said. He's going nowhere."
The five-eighth is contracted through 2026, and Marshall insisted the media glare had not influenced his decision to rest Galvin from Saturday's clash against Gold Coast.
The coach instead pointed to the youngster's need for a mental and physical break.
"He's been carrying a little bit of an injury in his hand this week, so it's just a bit of a rest to freshen up," Marshall, himself once the NRL's prized young half, said.
"You've got to remember, Lachie's 18 years old, coming into the NRL. He's played every game straight, bar the two he got suspended.
"It happens with a lot of kids, you go through ups and downs and lulls and sometimes they need a spell.
"We've decided this week was the week, regardless of the stuff that went on, he was going to have a rest this week anyway.
"He'll be back (against Canberra) next week."
Marshall insisted the club had Galvin's best interests at heart, following comments from Phil Gould this week that a full first-grade load was too much for a teenaged playmaker.
"We'll make decisions based on the best interests of our players," he said.
"You can say whatever you want, but unless you're here and understand, you don't know."
The Tigers will retire the No.1 jersey for Saturday's clash at Leichhardt Oval, their first at the ground since legendary Balmain Tigers fullback Keith Barnes died in April.
"(Barnes) was such a great man who loved the club a lot. It's only fair that we give that back to him," Marshall said.
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