Knights coach Nathan Brown confirmed the club's medical staff were with the 22-year-old, who was believed to be driving one of the vehicles involved in the crash in the M1's north-bound lanes at Cowan just before 10pm on Wednesday.

"Pauli has got a dislocated hip, but long-term, he's fine," Brown said on Thursday. Reports that Pauli also had suffered a broken leg were incorrect, he said.

"A dislocated hip is not great for him. I'm sure he's a little bruised, but I'm sure he will be fine and his welfare is obviously important to us," Brown said.

Emergency services arrived at the crash scene on Wednesday night to find seven wrecked cars scattered across the road and 10 people injured. Of those injured, eight people were adults and two were children.

The motorway was closed for three hours while emergency services treated the injured, and cleared the wreckage from the road.

The most seriously injured patient, a 66-year-old man, suffered chest and head injuries and was flown to Royal North Shore Hospital in a critical condition. He underwent surgery and his condition had improved to stable on Thursday morning, police said.

The two children were not seriously injured, police said, and were taken to hospital as a precaution.

A NSW Police spokeswoman said the Crash Investigation Unit was examining all of the circumstances leading up to the crash.

Initial investigations suggested three vehicles - a Toyota MR2, a Subaru Liberty and a Mazda Tribute - were travelling north on the motorway when they were involved in an initial crash, before those vehicles then crashed into four more vehicles.

The most seriously injured man was driving the Toyota.

Pauli was believed to be driving the Subaru with three passengers on board: a 27-year-old woman, who broke her leg; an 18-year-old man, who suffered suspected spinal injuries; and a 15-year-old boy, who broke his collarbone.

The driver of the Mazda, a 58-year-old woman from Gorokan, suffered a chest injury.

Police said a 50-year-old man, from Woy Woy, also was taken to hospital with chest pain; his 47-year-old passenger was checked for chest and neck injuries; while a 13-year-old girl was treated for bruising.

Pauli made his debut for the Newcastle Knights at the start of the 2016 NRL season, and played 15 matches for the club in both the front and back row. He previously played for the Parramatta Eels, as well as the NSW under-20s and the Australian schoolboys sides.

Brown said there was no indication how long Pauli would be sidelined for.

"I can't comment on any of that until we have a meeting with the medical staff. I'm sure he has got more tests that are required," Brown said.

He said the other Knights players were concerned for their teammate.

"Football clubs are like families, and all the guys are obviously [concerned] for Pauli," Brown said.

"I'm sure he will get plenty of visitors."

Pauli's injury comes in the same week that Knights player Jarrod Mullen was provisionally suspended for testing positive to an anabolic steroid.

Brown said he had spoken to Mullen directly, and he was sure he would "address the news when he's ready to do that. Whether that's in a day or two or 10, I don't know".

"Jarrod's welfare is, I think, everyone's main concern, not what's happened or how it's happened or why it's happened. I think as long as we can monitor Mullo's welfare, that's the main thing," Brown said.

Police have urged anyone who saw the crash on the M1 to contact Crime Stoppers on 1800 333 000.