A FIFA statement did not detail what the inquiry concerned but said it was not linked to the awarding of the 2022 soccer World Cup to Qatar - one of the targets of a series of wider investigations into corruption within FIFA that have rocked global soccer's governing body since last year.
The investigator also recommended a 20,000-Swiss-franc ($20,676) fine against Al-Mohannadi, in addition to the ban.
Al-Mohannadi, who is also the former secretary general of the Qatar Football Association (QFA), has not yet seen the FIFA report and so is unable to comment on it, a QFA statement said.
"However, he as well as the QFA are both confident that a full and fair review of the matter will confirm that he has cooperated extensively and candidly with the ethics committee and that any charges against him are without legitimate basis."
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The QFA also said it fully supported the candidacy of Al-Mohannadi for the next FIFA Council election.
The FIFA investigator's report will now go to the adjudicatory chamber of the Swiss-based FIFA Ethics Committee.
Switzerland has opened a criminal investigation into the decisions to award the 2018 and 2022 World Cups to Russia and Qatar respectively.
(Reporting by Tom Finn; writing by Maha El Dahan; editing by Mark Heinrich)
