INJURY KO FOR ROBERTS
The forward, who formed an impressive partnership with Lee Hughes last term, picked up the injury in a friendly with Cheltenham Town last Wednesday.
It was initially hoped that he had suffered severe bruising, but the worst was confirmed and he will be out for around eight weeks.
Speaking after having the tests, Roberts said: "I've been trying to smile since Wednesday night, but it just ain't happening.
"I'd had a really good pre-season, I was feeling really good, getting sharp and I was really looking forward to getting started.
"All that work is wasted now, and I'm going to be out. It's devastating."
Baggies boss Gary Megson will now have to plan for the season opener against Walsall without the 23-year-old former Bristol Rovers man.