SAO PAULO, Brazil (AP) — World soccer governing body FIFA said it was assessing the extent of damage to the stadium hosting the 2014 World Cup opener as officials inspected the grounds yesterday to determine what may have caused the deadly accident, just weeks before all stadiums for one of the biggest events in world sports were scheduled to be completed.

Two workers were killed Wednesday when a crane collapsed and a 500-ton metal structure toppled over part of the stadium in Sao Paulo, aggravating already urgent worries that Brazil won’t be ready for soccer’s showcase event next year.

FIFA wants all 12 World Cup stadiums ready by the end of December, and Brazilian news reports have cited unnamed workers as blaming the rush to finish the Arena Corinthians for the decision to raise the last missing piece of roofing on Wednesday, despite several days of heavy rains that softened the earth around the stadium.

The hypothesis that the rain-soaked ground might have ceded under the weight of the equipment is one of three main lines of investigation, said Brazilian media reports. Human error and a problem with the crane are the other hypotheses.

FIFA president Joseph ‘Sepp’ Blatter on Wednesday sent condolences to the families of those perished in the accident.