Robson felt her wrist give way during a morning practice session in Montreal, leaving her with no choice but to withdraw from the prestigious tournament at short notice.
The 19-year-old remains hopeful of playing in the US Open later this month, with a scan due later today to determine the extent of her wrist injury.
She told Tennis TV: "Well I practised this morning and everything felt fine and then I hit one routine backhand and felt something go in my wrist.
"We're not sure what it is yet, I've got an MRI scan later today. The physio team and I did everything we could to try and get on court but I just wasn't able.
"I don't know what's going on until the MRI but hopefully I'll be able to play next week and in the next few lead-up tournaments to the US Open."