The Bianconeri were always at a disadvantage from the moment they received a six-point deduction for alleged match-fixing in August, but seven months later Giuseppe Iachini's men are just two points away from leaving the bottom three.
Victory in a relegation six-pointer at Palermo last time out gave the Tuscans further reason to be cheerful and Rosina wants more of the same against mid-table Cagliari on Sunday.
He told acsiena.com: "We got a very important victory against one of our direct competitors.
"It was not easy but now we must think about the Cagliari game because that match will be just as complicated.
"We'll just focus on winning without worrying about the league table. Genoa are the closest team to us but beyond that I think we'll need a total of 40 points. We can do it."
Striker Nicola Pozzi and midfielder Simone Vergassola miss out against Cagliari due to injury but Iachini has an otherwise fit and suspension-free squad at his disposal.
Injured Cagliari midfielder Daniele Conti, meanwhile, will not feature Stadio Artemio Franchi while defender Luca Rossettini serves a one-match ban.
The Rossoblu issued a media blackout following last weekend's 3-1 home win over mid-table rivals Sampdoria.
Another victory behind closed doors at the Stadio Is Arenas was a positive move in the Sardinians' season but there will be no real relief until fans are allowed back into the newly-built ground for good.
One man who could talk to the press was Roman politician and super-prefect Achille Serra, who flew to Cagliari for crunch talks over the future of the stadium this week.
He told La Repubblica: "The situation is a difficult one but we hope the stadium will open its doors to fans for the Fiorentina game.
"Our plan will be presented at the weekend, we can't perform miracles but there is enough time to sort something out."
The islanders have not won at Siena since both sides reached the top flight in 2004, with the Bianconeri emerging 3-0 winners in last season's meeting.