The 19-year-old singer asked a Beverly Hills jeweller Neil Lane to design a 650,000 pounds creation to be gifted to Gomez on her 21st birthday, reported Daily Star.
Lane has supplied engagement rings to stars including Madonna and Britney Spears.
"Justin is planning to go through final designs with Neil in the next week. At the moment his favourite idea is a huge, canary yellow, princess-cut diamond surrounded by smaller diamonds and set in white or yellow gold," a source said.
Bieber is known to have kept his concert schedule clear for Gomez's 21st birthday. He is planning to fly back home from Boston on July 21, a day before her birthday.