The Duke of Sussex has been accused of making the Invictus Games a target for extremists by revealing he killed 25 people in Afghanistan.
Admiral Lord West, former head of the Royal Navy, called Prince Harry "very stupid" for giving details of his Taliban kills.
The retired admiral told the Sunday Mirror the Invictus Games – which are due to be held in Dusseldorf, Germany, in September this year – will now have "serious security issues" because of their direct connection to the Duke.
"The Invictus Games is very much labelled to him and so I would have thought the threat level there will definitely be higher," Lord West told the newspaper.
"There will be serious security issues because of what he said. Measures will have to be put in place to protect the veterans.
"And there will be people who, given half the chance, will want to do something."
The international multi-sport event for wounded, injured and sick servicemen and women, of which the duke is the patron, will now be a prime target for those wanting revenge, Lord West said.
"The Taliban will be reading (Harry's claims about killing fighters and) thinking there's this prince calling us all chess pieces and is quite happy about killing us.
"And there will be a lot of people, I am sure, in Islamic State and other terrorist organisations, who will think this is something which should be avenged."
Prince Harry has faced criticism in recent days since the excerpt from his memoir leaked about the number of insurgents he killed as a helicopter pilot.
Earlier in the week, a retired British Army colonel, famous for his inspirational speech on the eve of battle in Iraq, says the Duke of Sussex has "now turned against the other family, the military".
Colonel Tim Collins told Forces News: "This is not how we behave in the Army; it's not how we think."
"We shouldn't be attacking him"
Philip Ingram, a former military intelligence officer, feels people should have some sympathy for Harry.
Speaking to Sky News, he said: "A lot of the behaviours that I'm seeing of Prince Harry are almost triggers for me. They remind me of some of my behaviours whenever I suffered quite severe PTSD.
"We shouldn't be attacking him; we should be putting a big protective bubble around him because he's falling apart."
In his controversial memoir, Spare, which went on sale earlier than planned in Spain, Harry said that flying six missions during his second tour of duty on the frontline from 2012 to 2013 resulted in "the taking of human lives", of which he was neither proud nor ashamed.
The Daily Telegraph, which obtained a Spanish language copy of the memoir, earlier reported that Harry said he did not think of those he killed as "people", but instead as "chess pieces" that had been taken off the board.
"So, my number is 25. It's not a number that fills me with satisfaction, but nor does it embarrass me," he wrote.
The memoir is due for worldwide release on Tuesday, following his interview with ITV which is due to air later today in the UK.