Francis Tusa said he had "never seen a report as damning" after seeing the Government document.
Written by the Infrastructure and Projects Authority, Mr Tusa said the report states that vibration has caused hearing loss for some personnel testing the vehicle, while others suffered swollen joints and nausea after taking part in trials.
"Five of 12 recommendations are critical – as in without these the programme is doomed to fail," Mr Tusa added.
"The fact is, to get these fixed, it is going to take time. The only thing at the moment, and for the foreseeable future, Ajax can deliver is tinnitus."
Trials were paused between November 2020 and March this year due to concerns over the health of test crews.
According to Mr Tusa, the report shows the project is facing "major issues" which limit the time crew can spend in the vehicle to just 90 minutes.
There are also other design flaws which prevent the cannon being fired on the move, and the vehicle cannot go faster than 20mph.
The report supposedly sheds light on the delay of the Ajax programme, which was supposed to be delivered four years ago.
Retired Brigadier Ben Barry, Senior Fellow for Land Warfare at the International Institute for Strategic Studies (IISS), told Forces News the delay is "not academic".
He said: "It's replacing some clearly obsolete light armoured vehicles which were good in their day, but are now too small, too underpowered, not adequately protected and don't have adequate firepower.
"British Military commanders are going to be worried about this capability gap."
The MOD said it's still committed to the Ajax programme, with plans for Initial Operating Capability still scheduled for this summer.
There are 589 vehicles on order but, to date, manufacturer General Dynamics has only delivered 14 of the Ares variant – all of which are without turrets and odd sizes.
A defence source said: "One of the first things the Secretary of State did when entering office was to take a fresh look at Ajax.
"It was no secret the programme, that was originally contracted in 2010 and 2014, has had problems which is why the MOD has intensified scrutiny and work to rectify the issues.
"The Army, General Dynamics and the MOD is now engaged in an intensive round of assessments and rectification work to resolve any outstanding issues."
So far, £3.47bn has been spent out of a total budget of £5.5bn on the Ajax vehicle.
The report shows the Ajax is "undeliverable within the current budget," according to Mr Tusa.
"So the question is if it is to succeed and there is significant doubt it can ever succeed, is it going to cost what? An extra £1bn. £2bn. £3bn," he continued.
He added: "It is also worth noting that at no stage has the MOD ever been able to levy liquidated damages on the contractor General Dynamics."
Cover image: Ares variant of the Ajax armoured vehicle during a demonstration (Picture: British Army).