Lampard was hindered by injury in his first campaign in the United States, scoring three goals in 10 appearances, and fitness issues have also prevented him from playing a part for City in the opening four games of this season.
And Vieira confirmed on Thursday that the ex-England international will again be missing for Sunday's match against the Chicago Fire.
"He's not going to be fit for the weekend," said the Frenchman.
"I think we are a couple of days away from his comeback."
Lampard is yet to play for his new boss, and Vieira admitted that he feels for the 37-year-old as he battles this latest injury.
"When you are talking about a player of his calibre, it's always better to have him available to play games," the World Cup winner added.
"I'm feeling for him because he's a real champion and he's going through a difficult period, because of course he wants to be on the field, he wants to train and to help the team.
"He's missed training and it's not easy for him."
City face Chicago for the second time in just over a month this weekend, having won the previous game 4-3, but they are still looking for a first home win in 2016.