Damien Oliver has ridden Petits Filous in her four wins to date but was unable to ride the three-year-old at 51kg in the Moir Stakes, forcing trainer Ciaron Maher to look for a rider capable of making the light weight.
Maher booked Kerrin McEvoy to ride Petits Filous but the jockey earned a careless riding suspension at last Saturday's Caulfield meeting, providing Boss with the opportunity to partner the Moir Stakes favourite.
Boss said he had to work all week to make the weight but his current fitness meant he would comfortably shed the required amount in the coming days.
"A week's notice is fine because I'm ready to go,” Boss said. "Physically, I'm very fit and I just have to work a bit harder to get the weight off.
"I box three days a week anyway and do circuit work and sprints as well but I have a personal trainer anyway to help.
"At this time of the year, you get yourself really fit because you know there's going to be light rides.”
Boss had his first feel of Petits Filous at trackwork at Caulfield on Tuesday morning and the daughter of Street Boss stunned him with her quality.
"She worked over four furlongs (800m) finished her last two furlongs (400m) in a tick over 24 (seconds) and that was literally cantering,” Boss said.
"To look at her, she's not the most impressive horse to look at because she's not big but when you ride her, you go 'wow'.”
The withdrawal of Group I winner Terravista from Moir Stakes betting left Petits Filous as a $2.50 favourite on Tuesday ahead of her fellow Caulfield-trained three-year-old Fontiton at $4.40.
While bookmakers have Petits Filous as a clear favourite to remain unbeaten in the Moir Stakes, Boss was respectful of her opposition in the $450,000 contest.
"She's up and about but it's a really good race,” Boss said. "I know she has 51(kg) but she'll meet a few that can really gallop.
"That's why she's got advantage at the weights but she's quite the athlete. She can be anywhere in the run because she's very versatile.”