Monday 14 December 2015 15:18, UK
Saracens head coach Mark McCall confirmed on Sunday that Gustard has been approached by the RFU for a role within the England camp, though no official announcement has been made regarding his future.
Gustard is credited with Saracens' stern defensive ethic, and Greenwood believes his former Leicester team-mate will bring that same style to the England setup if he makes the move, and can match the pedigree of Wales' defence coach, Shaun Edwards.
"He's a good old-fashioned Geordie," said Greenwood. "He's a grafter, and he brings an element of enthusiasm, fun and dynamism back.
"Gustard has developed 'the Wolfpack'. I think [he] can rival Shaun Edwards for creating an international defence with bite, venom and the ability to change a game.
"Martin Johnson's brain is the size of a planet when it comes to all things rugby, and he was discarded and we haven't seen him since."
Another coach rumoured to be in the running for a role within the England staff is Steve Borthwick, who played for Eddie Jones when the Australian was coach of Saracens.
Borthwick also worked under Jones as forwards coach of Japan during the World Cup this year, helping the Brave Blossoms to wins over South Africa, Samoa and USA during their campaign, and Greenwood says that experience will help the 36 year old in a role with England.
"What you're going to get with Borthwick is a codebreaker," said Greenwood. "A man who has incredible diligence about his job, and will work extremely hard to make the England setup in the set piece and in the forwards a hugely competitive one.
"As he did under Eddie Jones with Japan. He has that experience now of coaching in a World Cup.
"He's a very calm, assured character - backs himself."
The 2003 World Cup winner says it's understandable that Eddie Jones would want to bring his own coaches into the England camp, but has urged the RFU to ensure that the experience of England's outgoing coaches does not go to waste.
"It's a heck of a lot of experience. A couple of British and Irish Lions coaches, some Lions players, some World Cup winners, but [they] seem to have been stigmatised with the epic failure in the World Cup - not getting out of the group stage.
"A coach would tend to bring in new voices. His own men. It certainly happens in football, we shouldn't expect much different in rugby.
"But, if there's one plea to England Rugby and Ian Richie - don't let these guys just go into the wilderness. Don't just give them a P45 along with Stuart Lancaster.
"Please don't let these guys disappear like they let Martin Johnson disappear. It was a crying shame.
"Martin Johnson's brain is the size of a planet when it comes to all things rugby, and he was discarded and we haven't seen him since.
"It would be an utter dereliction of duty if these guys disappear into the ether."
