Korean Kim Ji Hyun left her position as India's women's singles coach after less than a year in the role, in order to be with her ailing husband in New Zealand.
"It is true, Kim has resigned as her husband is pretty unwell," India's chief national coach Pullela Gopichand toldPTI.
"He suffered a kind of neuro stroke sometime during the World Championship. So she rushed back. She needs to take care of him as it will take around four to six months for him to recover."
Restoring Sindhu to form
Kim's resignation will come as a major blow to the Rio 2016 silver medallist.
In August, the 45-year-old was pivotal in guiding Sindhu to a first World Championships gold medal in Basel, Switzerland.
The pair had developed a good relationship, with the Indian shuttler acknowledging her improvement under Kim after that victory.
"It is unfortunate that Kim had to leave at this stage. I wish her husband a quick recovery" - Sindhu to First Post.
"I had a good rapport with her and I know it will be a fresh start for me but it is something which is part of a sportsperson's life. I will have to work harder and I am sure Gopi sir and the BAI (Badminton Association of India) will take care of everything."
One option for a replacement coach is the Indian men's singles coach Park Tae Sang.
A golden opportunity
Despite the setback, Sindhu's form going into the Tokyo Olympics is better than when she won silver four years ago.
As such, many Indians will be hopeful that their badminton star can win the nation a second individual Olympic gold medal.
“I think it would be fair to say that she would be one of the big contenders for the gold medal,” Gopichand told Reuters.
“But having said that, there is competition, and it just gets more for Sindhu because she will be the target, people have a year to plan against her."
“So, of course, she needs to train, she needs to evolve, she needs to add new thinking to the armoury and that’s very important.”