It's the same knee Slater injured during the 2012 State of Origin series when he suffered posterior cruciate damage that sidelined him for almost two months.
Slater said early indications were that this was a recurrence of that same injury.
Australia will play their semi-final at Wembley next Saturday before the final at Old Trafford in Manchester on November 30.
Slater said it was too early to know just how bad the injury was until he gets the scan results tomorrow.
"It's a bit sore. There's not much I can do about it," he said.
"It's the leg that I did in the second State of Origin last year. It seems like the same injury. I suppose that's a good thing because the PCL isn't functional anyway.
"It's a classic PCL injury. I had a grade three PCL last year. Although my knee was hitting the ground last year it was in the same position.
"I knew straight away what it felt like. Hopefully the scans came up good and I'm a chance of playing again in the tournament. That remains to be seen.
"I suppose the only concern is the cartilage now and we'll know more from the scans."
It caps off a terrible week for Slater after he was involved in a fight outside a Manchester nightclub while out celebrating in the early hours of Monday.
Slater was taken into custody by police but later released without charge.
Asked if it was a disappointing way to finish the week, Slater said: "Sure is."
Coach Tim Sheens said it was too early to call on Slater's future in the tournament.
"We haven't given up thought he might still be available. If not this week possibly after (for the World Cup final)," Sheens said.
"I'm not going to panic just yet."
If Slater is ruled out for the tournament Inglis will obviously remain at fullback which opens up opportunity for Michael Jennings and Josh Morris to come into the top side at left centre for the semi-final.
Inglis put in a powerful performance last night and admitted he was excited about the prospect of playing fullback again, although he was clearly disappointed for Slater.
"It definitely is. Hopefully the scans come back all clear," Inglis said.
"In the end he is a valuable member to this team. To see him go down like that was disappointing but like I said hopefully we see the scans come back all clear."
Inglis admitted he went out with a plan last night get more involved and the Americans found him just about unstoppable as he scored two tries and set up two more.
Asked if he would relish the chance to play fullback again next week, Inglis said: "I would love to wear that number one but I am not the coach. A lot happens in a week so we will just have to wait and see."
The injury to Slater overshadowed another impressive performance by the Kangaroos who now haven't conceded a try in their last three games.
Australia raced in eight first half tries all up including four to Brett Morris that equalled a World Cup and Australian Test record.
Hayne then joined him in the record books when he finished with four tries adfter scoring the first try of the match and then a second half hattrick.
Sheens had overlooked Brent Tate, Josh Morris and Jennings for the right centre position but Hayne's performance more than justified the coach's gamble.
As good as the Kangaroos had looked in the pool games, last night was by far their best attacking performance of the tournament.
Skipper Cameron Smith and Cooper Cronk were the other try scorers while Brett Morris was the official man of the match and Matt Scott had a powerhouse game up front after being rested last week against Ireland.
