FIFA says Qatar's desert heat could put players' health at risk at a 2022 World Cup, and the United States bid needs stronger guarantees of federal government support.
FIFA's technical panel says 2018 candidates England and Spain-Portugal are "low-risk" options, though Russia faces challenges on providing transport infrastructure. The panel's reports highlight concerns after making four-day visits to all nine bidders to evaluate their ability to host a World Cup.
The assessments are designed to help FIFA's executive committee choose the hosts in a December 2 secret ballot.
FIFA's ethics committee will announce on Thursday if two of the 24 voters and the Qatari and Iberian bids should be barred for alleged corrupt vote-trading deals.