According to The Sun, the 'OMG' singer was seen at New York outlet Andrew Buckler buying a sweater, jeans and a shirt for the teen star.
A source said: "He told the staff he was shopping for Justin. He was talking about Bieber's clothing size to make sure he would get the right fit for him."
Bieber had previously joked that he hoped Usher would buy him a motorbike, after he had been given a Range Rover for his 16th birthday.
