Fuller was rushed to hospital during the 2-1 defeat by Bolton on Saturday following an awkward fall at the Reebok Stadium. It was the second time in three weeks that the striker has had problems with his shoulder. He was also hurt at Newcastle.
Pulis believes fears Fuller's recent absence on international duty for Jamaica did not help.
"He's fallen heavily on the elbow and so the shoulder has most probably popped out again," the Stoke boss told the Sentinel.
"The problem is, when they go on international duty they are taken away from what we do on strengthening work, like Ric on his shoulder. If they're away for 10 days you don't know what they're doing."