Bolt is set to defend his world sprint double title at the Beijing World Championships in August.
However, Bolt’s withdraw from the Jamaica Senior Championships, along with Diamond League Meets in Paris and Lausanne, raised concerns.
"What I can say is I'm very concerned about the progress of his preparation so far," Mills told Reuters.
"But as to between now and Beijing that depends on what I learn when I have the discussion with the doctor."
According to Mills, “for several weeks now he has been complaining and he has been restricted in his training by the complaints, hence it triggered the trip to the doctor.”
According to a release from Bolt’s team, “the 28 year old Jamaican has been feeling discomfort in his left leg since his last competition which has restricted his training.”
“He visited Doctor Müller-Wohlfahrt in Munich who confirmed that he has a blocked sacroiliac joint which is restricting his movement and putting pressure on his knee and ankle,” the release said.
“I’m disappointed not to be able to compete in Paris and Lausanne. I love running at these meetings but at the moment I am unable to compete at 100%. I look forward to getting back into full training as soon as possible”, said Bolt.