Vieira told Feel Football: "Thierry Henry is a huge player and it is a big blow for the club to lose him, certainly.
"When I left Arsenal I know they had good quality players in midfield to come in - they had Cesc Fabregas to replace me. They have good quality players up front too, with (Robin) van Persie, who has been injured but is really good, and (Emmanuel) Adebayor. They have the quality to do well, but it will not be easy.
"You have to remember, when Thierry came in he had to replace Ian Wright, which was not an easy thing to do!
"He achieved that and broke all the records, so the person who will take over from Thierry will be in the same position. They will need to do the same thing he did.
"It is important to know that nobody is bigger than the club itself and I hope Arsenal will keep progressing. The club can still progress and they are in a good position. They have a new stadium and all big clubs have a big stadium, so now they need to get the results to be at the very top."
Henry, used to being the undisputed star man at the Emirates Stadium, now finds himself just one among many established superstars of the world game at Barcelona.
But Vieira feels his international team-mate has the quality to shine at the Nou Camp next season.
"There are no doubts, he will be very, very good at Barcelona," Vieira said.
"He is a quality player so I am sure he will fit in very well. People are talking about how he will play with (Samuel) Eto'o and I don't think there will be an issue. To have Henry, Eto'o, (Yaya) Toure, Ronaldinho and (Lionel) Messi in the same team is just fantastic."