There are fears that Naismith tore his ACL late in the game in what has been a wretched run of injuries for the big man.
The 27-year old missed all of the the 2018 and 2019 seasons with knee problems and now looks set to miss the rest of 2020.
Naismith will undergo scans today to confirm the injury, but the club fears the worst.
“Unfortunately we think he’s done his knee,” a dejeted John Longmire told reporters post-match.
“We’ll confirm it with a scan but it looks… yeah it looks like he’s done his knee.
“It was in the last quarter at some stage, I’m not exactly sure, I only spoke to him briefly.
“He missed two years of footy and he come back and plays Round 1 and plays really well then obviously the break. He lost his sister (Kristi to pancreatic cancer) through that break and then he comes back and does his knee.
“It’s a terrible run for him.”
Asked what he would say to Naismith to comfort him, Longmire replied: “There’s nothing you can say. You’ve just got to be there, sometimes it’s just sitting there,” he said.
“We need to give him to time to digest it. It obviously has to get confirmed but he needs some time and we’ve got to be with him and look after him.
“He’s had a terrible run in a number of ways so we’ve just got to look after him.”