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"With confidence I think he's (Williams) the finest winger in world rugby, but at this precise moment in time, on the back of his ankle injury, the way he's been playing and his defensive lapses, I've decided to leave him out," said Greenwood, after he and fellow Sky Sports Rugby Club pundits Stuart Barnes and Dewi Morris aired their opinions on the best Britain and Ireland have to offer.
"I've gone for the bigger burlier type of winger in Jamie Roberts. Let Shane Williams come off the bench and do his stuff."
Williams may only be on the bench when it comes to Greenwood's dream XV but a fellow Welshman heads the list when it comes to guaranteeing selection.
"I think Gethin Jenkins is going to be the cornerstone of this Lions pack," added Greenwood.
"How he hasn't been named as one of the top three players in the Six Nations I don't know. He's been absolutely wonderful for Wales in the tight, the set piece and also the loose.
"Jenkins is a big carrier, has a tremendous work-rate and is a fantastic tackler. If we're talking about Pierre Spies, John Smit and Schalk Burger, you want a prop forward who is running around and making tackles.
"For all the wonders of (Paul) O'Connell and (Brian) O'Driscoll, my first name on the teamsheet is Jenkins."
Gethin Jenkins has the backing of Stuart Barnes, Dewi Morris and Will Greenwood
Barnes, Greenwood and Morris agreed on eight of their starting line up with all three handing Brian O'Driscoll the captaincy and pairing Paul O'Connell with Alun Wyn Jones in the second row.
Stephen Jones, Riki Flutey, David Wallace, Tom Croft and Jenkins were the other players given the vote of confidence by all three pundits, with Wallace named at No8 by Barnes and Morris and on the openside flank by Greenwood.
"You're going to need a few warriors out there, which is why I've put Phil Vickery in, and Delon Armitage has had an outstanding Six Nations and will thrive on the hard ground," said Barnes when explaining his choices on Sky's Rugby Club.
"Tactical decision-making is going to be very important, which is why I've got Jerry Flannery at hooker, O'Connell in the second row and David Wallace at No8. They're decision-makers and that's what you need against the Springboks.
"I've gone for Wallace at eight because I think Jamie Heaslip is a pale imitation of Pierre Spies, Andy Powell isn't bright enough and Nick Easter isn't quick enough. We've seen Wallace do it so many times for Munster and I think he's at the peak of his game. He's quick, powerful and he'll thrive in South Africa.
"That also means you get Martyn Williams at seven. The best back rows in Britain and Ireland are Williams and Wallace and I want them both in my team."
David Wallace, a Lion in 2001, earns a starting place in all three line ups
Following Tommy Bowe's try-scoring heroics in Ireland's Grand Slam triumph against Wales, Morris is keen to see the Ospreys wing make even more headlines in South Africa.
The ex-England scrum-half, who toured New Zealand alongside Barnes in 1993, has named Bowe in an all Ospreys back three that also includes Williams and Lee Byrne.
In the only position in which all three former Lions disagree, Morris names Sale's Dwayne Peel at No9, while Barnes and Greenwood plump for Mike Blair and Mike Phillips respectively.
"One guy I definitely want to see in there is Bowe," said Morris, who made eight appearances for the Lions 16 years ago, playing in all three internationals against the All Blacks.
"I think he's been tremendous. His appetite, coming in off the wing looking for the ball is sensational. He's quick, aggressive and will thrive coming up against the likes of Bryan Habana.
"I think Mike Phillips' form has gone down, as has Mike Blair's from the autumn.
"I know Peel has been carrying an injury but I think he's an all-rounded scrum-half. He's got a good head, hands and feet and if he gets back to good form and fitness he will cause problems for any defence."
Morris believes Ireland's Six Nations hero Tommy Bowe has to start against the Boks
Ireland's Six Nations clean sweep hasn't been reflected in a similar dominance of the sides selected by the former Lions trio, however, with the first two pundits selecting only four Irishmen in their starting XVs and Greenwood picking five.
Welshmen dominate the lineups, with Morris naming seven Wales stars and Barnes and Greenwood selecting six apiece.
All four countries are represented in each of the three XVs, something that didn't happen in any of the last three Lions Tests on the 2005 tour of New Zealand.
Stuart Barnes' Lions XV
15 Delon Armitage
14 Jamie Roberts
13 Brian O'Driscoll (c)
12 Riki Flutey
11 Shane Williams
10 Stephen Jones
9 Mike Blair
1 Gethin Jenkins
2 Jerry Flannery
3 Phil Vickery
4 Alun-Wyn Jones
5 Paul O'Connell
6 Tom Croft
7 Martyn Williams
8 David Wallace
Dewi Morris' Lions XV
15 Lee Byrne
14 Tommy Bowe
13 Brian O'Driscoll (c)
12 Riki Flutey
11 Shane Williams
10 Stephen Jones
9 Dwayne Peel
1 Gethin Jenkins
2 Ross Ford
3 Euan Murray
4 Alun-Wyn Jones
5 Paul O'Connell
6 Tom Croft
7 Martyn Williams
8 David Wallace
Will Greenwood's Lions XV
15 Lee Byrne
14 Tommy Bowe
13 Brian O'Driscoll (c)
12 Riki Flutey
11 Jamie Roberts
10 Stephen Jones
9 Mike Phillips
1 Gethin Jenkins
2 Jerry Flannery
3 Euan Murray
4 Alun-Wyn Jones
5 Paul O'Connell
6 Tom Croft
7 David Wallace
8 Jamie Heaslip
