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Caley Thistle lie five points adrift at the bottom of the Premiership with just five games of the season remaining.
"It's massive," Foran told BBC Scotland. "Biggest game of my career, biggest game of the players' careers.
"Ross County [are] probably out of the relegation battle but we can drag them back into it."
The recruitment of former assistant manager Maurice Malpas last week was designed to address defensive problems.
Foran concedes that it was the club's directors who proposed the idea of adding more experience to the coaching team, but insists that he identified Malpas as the man to appoint.
"The board thought it would help by bringing someone else in," Foran said. "An older, more experienced person.
"We're all trying to fix the problem. I had a think who was out there, who I could trust, who had the game knowledge and Scottish Premiership knowledge, so I picked Maurice.
"The board recommended I bring someone in. There was no problem with that."
With just four wins from 33 league fixtures, retaining their top-flight status seems an uphill task for Inverness, particularly given their record of conceding more goals than any side in the Premiership.
"Defensively as a team, it hasn't been good enough," Foran said.
"[We've] probably been too open at times attacking, so we've worked on that. There's obviously been a problem; we've conceded too many goals.
"Maurice has over 50 caps. He's managed, he's been assistant manager. But the main thing for me, you can always trust Maurice.
"He's old school and is never going to stab you in the back. He'll always say it straight to your face and he's good to have around the place."

The 14-month old tabby and white called Pumbaa was found bleeding in a Peterborough alleyway on Saturday.
The stab wound was so deep the vet was unable to operate before Pumbaa died.
A second cat - Mischief - was shot by an air rifle in an area near to where Pumbaa was stabbed, according to the RSPCA.
It is unclear whether the two incidents are linked.
RSPCA inspector Justin Stubbs said: "These were two shocking and completely senseless attacks."
Pumbaa's owner, Kirsty Cracknell, 29, of Croyland Road, said: "I am utterly devastated about Pumbaa - he was such a soppy little mummy's boy. I just keep expecting him to jump through the window.
"What particularly breaks my heart is that I think he must have been on his way home to me, considering where he was found."

The city centre road was made pedestrians only from June to November during the redevelopment of the Westgate Shopping Centre.
Now Oxfordshire County Council has agreed to continue the policy when the centre reopens because of the predicted increase in pedestrians.
The "experimental traffic order" still has to be signed off by the government.
The closure has also been blamed for increasing pressure on other city centre roads.
When the shopping centre is finished next year there are expected to be 11 million more people using it.
Council officers have estimated the number of pedestrians using the road will increase by 145% from 4,000 per hour up to 9,800 per hour.
They have also calculated that at present, 48 buses per hour use the road.
Officers said in their report that assurances from the bus companies "do not remove our concern over pedestrian safety".
But transport boss David Nimmo Smith said he was worried it would cause increased bus traffic in other roads such as St Aldates, which he described as an "architectural gem".
The Secretary of State for Transport will now have to approve the plan before it comes into effect.
Inverness Caledonian Thistle manager Richie Foran insists Friday's Highland derby against Ross County is the most important match of his career.
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