The 400m hurdler has caused more than a little bit of consternation in the Great Britain ranks in the Games build up due to his struggles for form in 2012.
A winter operation and some untimely illnesses mean the Welshmen will arrive in the capital without a single win to his name, apart from in purely domestic fields at the UK Championships, where he booked his Olympic spot.
Greene again finished second in the Diamond League meeting in Crystal Palace behind the undefeated 2012 world leader Javier Culson after an identical result in Paris the week before.
On that occasion in France, Greene ran a personal best of 47.84 seconds, while clocking 48.10 in London, his third fastest ever, with his Puerto Rican rival clocking 47.78 on both occasions.
However, Johnson is warning the Swansea athlete that his Crystal Palace heroics will need to be significantly improved upon if he is to add Olympic gold to his Commonwealth, European and world titles.
"The event is just full of people who have done it at championship level," said Johnson, who was speaking following the launch of his new mobile phone apps, Michael Johnson's Motiv8 and Michael Johnson's Fun Run, which are aimed at the health and fitness market.
"It's going to be tough. Dai Greene had a personal best this year and still got beat. He knows now the only way he takes home gold is with a personal best.
"The 400m hurdles is one of the toughest events in all of track and field right now because there are so many great competitors.
"If the preliminary qualifying rounds go the way that we all probably think they should go, barring anyone having a disaster, you'll have nearly every lane with a world champion or a former Olympic medallist.
"You've got Javier Culson, two-times world championships silver medallist. He's probably the favourite.
"You've also got Angelo Taylor in there who's a two-time Olympic gold medallist in the event. You've got Felix Sanchez who's an Olympic gold medallist and then of course Dai who is the world champion and European champion."
As if Greene's challenge weren't big enough the 26-year-old will also have to deal with the added expectation a home crowd brings.
Johnson's crowning glory came in Atlanta in 1996 when in front of a home crowd he stormed to gold in both the 400m and 200m, a double that has never been accomplished before or since at the Games.
And the 44-year-old, whose world record for the 400m set in Seville in 1999 still stands to this day, is backing Greene to follow in his footsteps.
"Dai's not afraid and he likes the challenge, and understands pressure and how to deal with it, which not everyone can say," added Johnson. "I don't think the pressure of being the home favourite will affect him."