Marin, a prime contender for the gold medal at the Tokyo Games, suffered a torn anterior cruciate ligament in her left knee during training and pulled out of the showpiece event on Tuesday.
“So sorry to hear about your injury. Hoping that you will recover soon and come back stronger,” Sindhu, who had settled for the silver medal at the Rio Games after losing to Marín in the final, said in a video message posted on twitter.
Recalling the epic final match, Sindhu said: “I remember the last Olympic Games when we played in the final. It was really good competing against you so I’m going to miss that again, and I’ve been missing you, seeing you on court.
“I will miss you at the Olympic Games but hope we compete against each other soon, so come back fast and recover soon. Lots of love.”
The 27-year-old from Spain felt discomfort in her knee during training on Saturday and tests later revealed that it’s an ACL injury.
Marin had earlier suffered an ACL on her right knee in January 2019, which kept her out of the courts until September of that year.
Marin, a three-time world champion, was a title favourite as she had been in red-hot form this year, winning four of the five finals that she played.