Mills told Reuters that the right hamstring injury sustained by Blake during a 100m race on Saturday at the UTECH Track and Field Classic in Kingston was more serious than originally thought.
"An MRI done Monday afternoon revealed the hamstring injury sustained was more serious than first thought," he said. "Blake could be out for several weeks as he recuperates."
Blake, who finished second to training partner Usain Bolt in last year's London Olympics 100 and 200 metres final, trailed former world champion Kim Collins of St Kitts & Nevis after 40 metres following a less than impressive start in his first 100 of the season on Saturday.
The joint second fastest man ever then pulled up, favouring his right hamstring as he tried to power past Collins.
Blake who walked around without assistance minute after the race, tweeted "am good my twitter family just a cramp". He was scheduled to run over 200m in Shanghai.