Tevez is set to join Brazilian side Corinthians in the summer after the two clubs agreed a fee for the striker.
“It is never easy to lose players like Carlos Tevez,” said Vieira.
“In the last two years he has been fantastic for the football club, scoring goals.
“The club has grown that fast and Carlos has made a huge contribution to it, like all the players.
“But in football, it is not the first time a big club has lost a big player.
“I believe we can still achieve our targets and we will still have a really competitive team.
“The players will take more responsibilities on their shoulders and that will make them better players.
“If Carlos does leave we just have to wish him good luck and say thank you for everything he has done for the football club.”