Speaking at the Vale of Glamorgan Training Centre, Tom James said, "We've had the results of the scan back and although I won't need an operation to repair the shoulder damage, I'm still not expected to be back on the rugby field for four months.
"It will be a case of working hard with the physiotherapist to try to strengthen the shoulder."
The news is a blow to the young winger who picked up the Cardiff Blues Most Promising Player of the Year Award in May.
"I will have a rest for three weeks now and return to pre season training with the Blues, where we will begin the treatment," added James who impressed with his power and pace in both Tests against Canada and USA.
"I enjoyed the tour of North America and was happy with my form. I was really pleased to have started both tests and scoring two tries was a bonus."
"It is frustrating that I picked up the injury as I felt I was playing well but hopefully I can get back sooner rather than later."