Webb, who was Concacaf president for three years from May 2012, was banned for life and fined one million Swiss francs ($1.056 million, €856,000) by the FIFA adjudicatory chamber in September 2016 for offenses including "conflict of interest" and "corruption".
Ex-Fifa vice president Webb, 53, appealed against the fine but world football's governing body announced on Monday that his appeal had been rejected.
Read also: Who's who in US Fifa corruption probe?
He was arrested in Zurich in 2015 and extradited to the United States, where he pleaded guilty in an American court to charges including fraud, money-laundering and racketeering and agreed to forfeit $6.7 million (€5.4 million).
Webb, who was president of the Cayman Islands FA at the age of just 26 and became the youngest ever football confederation boss when he took over at
Concacaf, is still to be sentenced in the United States.