Wellington announced the signing of the 28 year-old centre-back on 9 August.
Having played in the Serie A with Parma and Sampdoria, and more recently in Serie B, Rossi's first week with the Phoenix has been met with positive reviews from new teammate Moss.
"His fitness is great. These guys in Europe keep themselves in top shape, you can tell," Moss told The World Game.
"He arrived looking lean and well and joined straight into training.
"He hasn’t needed any extra time or special treatment as such. He’s in his second week of training with us now.
"He’s definitely a terrific signing, going on the first couple of weeks, and he’s learning more and more about how Ernie wants us to play and he’ll be even better as we go along.
"We had a problem last year when Jeffrey Sarpong came in and he needed a few extra weeks to get up and running because he was having some niggling injuries, but Marco has come in fit and strong, and is fitting in well with the lads."
Wellington coach Ernie Merrick needed to recruit an experienced centre-back after the retirement of Ben Sigmund at the end of last season.
He embarked on a painstaking search for the right man and, on pedigree, he looked to have succeeded.
Considering Rossi's arrival in Wellington, the word from Moss will be further encouragement for Phoenix fans who were already hoping for a return to the finals after the dual signing of former Melbourne Victory stars Kosta Barbarouses and Gui Finkler.
While there has been language difficulties in the early stages, Moss is confident they won't be an issue.
"Marco’s English is very limited, which has been a challenge initially, for the first few training sessions," he said.
"But you don’t really have to give him too much coaching or instructions.
"He’s very experienced and really comfortable on the ball - his positioning is awesome.
"He just sits next to ‘Dura’ (Andrew Durante) there in the central defence and he’s looking good so far.
"We’re lucky over here because our youth team coach (Valerio Raccuglia) is Italian.
"Valerio has been shadowing Marco at training and team meetings and translating to him, so all the important information is getting across.
"And in amongst the boys - we have a couple of guys, Dura and Vinny (Vince Lia), who speak a little bit of Italian.
"We’ve taken Marco out to lunch a couple of times as well, and gone to our favourite Italian restaurants, but he says it’s not as good as home so maybe we need to find some new ones!
"The foreign players usually pick up the language pretty quickly, being in and around the boys every day.
"We had Daniel, a Brazilian, a few years back and I remember when he first got here he didn’t speak a word of English and had his brother stay with him for a month.
"But he picked up the language and after a couple of years here his English was fluent. He still rings the boys for a chat."
Moss said he didn’t anticipate anything stopping himself, and the rest of the Wellington players, from quickly developing the necessary understanding with Rossi in games.
"If it was a less experienced player the language thing might be a problem," Moss said.
"But Marco has been playing in front of me in training games and I don’t have to give him instructions. He’s already there, his positioning is really good.
"He gets his head up when he’s on the ball, so he makes the right passes, whereas if it’s a young centre-back you’ve got to help them out with their options and where they’re going to play and things like that."
Moss said captain Durante was already feeling very comfortable with his new playing partner.
"I know Dura is happy," he said.
"He especially wanted a bit of tall timber next to him and Marco is certainly that.
"Hopefully, Marco will be able to pop up down the other end on set pieces and score a couple of goals as well.
"It’s going to be good to see him play in a game now.
"We’ve got a trial coming up against a local Central League selection side in Kapiti on 27 August and then we’re off to Townsville to play Melbourne City up there on 11 September, so I’m sure we’ll see him in action then."