The former St Helens and Great Britain scrum-half, 35, who retired 12 months ago and subsequently joined the Salford coaching staff, was registered by the Reds earlier this month when the club sold Matty Smith to Wigan.
At the time head coach Phil Veivers said he would only select Long in case of an emergency and that looked to be the case when Sneyd was taken to hospital for x-rays amid fears that he broken a leg in the Reds' 34-26 defeat by Hull.
However, the 21-year-old Sneyd has been cleared of major injury and has not yet been ruled out of Saturday's game against London Broncos at the Twickenham Stoop.
"We're waiting for him to come in for treatment but I'd say it was just bruising," Veivers said. "Longy was registered as cover so he'd be playing if Marc Sneyd had broken his leg but we'll ice him up and see how he is. I'll be giving Marc as long as possible to prove his fitness."
Long hung up his boots after an injury-hit couple of seasons with Hull but has maintained his fitness and began playing rugby union with National League North 2 side Preston Grasshoppers last season.
Meanwhile, Veivers admits he is concerned over growing rumours linking his other half-back, Australian Daniel Holdsworth, with a move away from the City of Salford Stadium.
Holdsworth, man of the match in the Exiles' win over England earlier this month, is contracted to the end of 2013 but that has not prevented speculation growing over his future, with Hull the latest club to be linked with him.
"You are always worried," Veivers said. "He's contracted to us but they say there's no smoke without fire.
"You always want to keep your better players but I've already lost Matty Smith and I'm losing Sean Gleeson (to Hull KR)."