Reports this week said prosecutor Stefan Palazzi has filed an appeal against nine people, including Di Vaio, who were acquitted of wrongdoing last week. The appeal is to be heard in a federal court on Monday.
''When you think things are settled and done, it pops back up,'' coach Jesse Marsch said Wednesday. ''All indications are that this will be OK, but the last time took us for a bit of a turn.
''He seems to be focused in a good way. And we're all pretty hopeful that it's going to work out in favour of him not being suspended.''
Palazzi had asked that Di Vaio be suspended for a year for failing to report an alleged attempt to fix a match between Bologna, his former team, and Bari in Italy's Serie-A in 2011.
Among players also named in the appeal were Juventus stars Leonardo Bonucci and Simone Pepe over suspicious matches they played with their previous clubs.
''The prosecutor has appealed everyone,'' said sporting director Nick De Santis. ''It doesn't worry us or Marco. His lawyers feel that he won't have to go back again.''
Di Vaio, who was not made available to the media on Wednesday, was signed in mid-season as the expansion Impact's first designated player, or one paid more than the maximum allowed under the Major League Soccer salary cap.
The 36-year-old debuted in June, but it took until a 3-1 win over New York in late July to score his first MLS goal. He missed the following game to return to Italy for hearings, and was elated on his return to learn he was acquitted.
He was held off the scoresheet as Montreal won a third game in a row at New England on Sunday. Their next test is at home on Saturday against the first-overall San Jose Earthquakes.
Di Vaio has said the Italian investigation has had nothing to do with his scoring woes, and De Santis agreed.
''I had a conversation with (Los Angeles coach) Bruce Arena about when a DP comes in mid-season and how difficult it is for him to adapt to MLS,'' he said. ''Really, I'm not worried about Marco.
''As of today he's got one goal, but just what he's brought when he's on the field, you can see he’s a player at another level. And with everything that's gone on for him, it hasn't been easy for him. But on the field and in the dressing room, he's very, very positive and with his level of play, he's brought people to their feet and you feel the fans are all behind him.''
De Santis said Di Vaio contributes to the team even without scoring.
''With his final passes and his ideas on the field, he's making guys around him better,'' he said ''You see the difference.''
One who would agree is forward Sanna Nyassi, a second half substitute who scored a stunning goal late against New England. The Gambian striker went on a run up the middle, eluded a defender and blasted a shot to the top corner. The much-replayed strike is a candidate for MLS goal of the week.
''As soon as I won the ball, I knew Marco would make that run,'' said Nyassi. ''It was a great run by Marco and he took the other defender with him.
''So I went one-on-one, beat the other guy and took the shot. I think that was the best goal I've scored since I've become a professional. I think it's my best goal ever.''
Another player to draw attention this week was French defender Hassoun Camara. Reports said he has drawn interest from second division clubs in France and England, including Crystal Palace and Leeds United.
Camara, whose contract is up at the end of this season, said he hopes to stay in Montreal.
''Personally, I have no intention of leaving the Impact,'' he said. ''I've also heard there have been rumours, or interest from elsewhere, but I haven't signed anything yet.
''Right now I'm here. I'm happy here and I hope to stay here next year.''
Camara played for Marseille in France's top league and Bastia in the second division before joining the Impact last year when they were in the NASL.
He was bumped from his natural position in the central defence when the Impact signed former AC Milan star Alessandro Nesta in July and when Nelson Rivas and Matteo Ferrari returned from injuries. But his speed and athleticism have proven useful at right back.
Captain Davy Arnaud, who has a stiff neck, and Nesta did not practise Wednesday but are expected to play.