Ex-NBA star Ray Allen suffered gnarly injuries in a bicycle crash over the weekend … and he says the accident was so bad, he could’ve been SERIOUSLY injured if he weren’t wearing his helmet.

The 2-time NBA champ spelled out the scary details of the incident on his social media page Sunday … saying he was riding his bike in his neighborhood when a car pulled up behind him.

“As I looked back behind me,” Allen said, “the car was gone, but, the minute I turned my head back to what was in front of me, it was too late.”

Allen says he crashed into a tree branch and was violently thrown from his ride.

“I landed on my face, shoulder and hip,” Allen said.

The 45-year-old says he was able to get up after the crash and walk to his house … but he claims that’s when he lost his breath and nearly passed out.

“My wife immediately took me to the hospital to make sure that I didn’t have any internal bleeding,” Allen said. “Had my vitals checked and a few X-rays taken and all was ok.”

But, Ray did have some gnarly injuries … Allen showed photos of bloody road rash on his leg as well as a big scrape on his shoulder.

Allen also showed a pic of his helmet, which clearly took a large brunt of the blow in the crash.

“Thank God for my helmet because as you can see in the picture my head hit the ground and I didn’t even realize it,” Allen said.

“My helmet saved me from a far worse fate.”

Allen says he was hesitant to share the incident but wanted it to be a reminder to everyone to wear helmets while riding.

Several NBA stars reached out to the 10-time All-Star expressing gratitude for his health … with LeBron James writing on his social media, “Glad you’re good my brother!!!”

Ex-NBA star and cyclist enthusiast Reggie Miller also sent his well wishes, saying “Welcome to the club, HELMETS HELMETS HELMETS!!! Speedy recovery my friend