Eze is back after a post-season achilles injury.
"Obviously he's a talented player but he's still a long way to go from his best," Vieira said.
"We have to remind ourselves that he will need time to return to what he was because of the injury. But he will get there. He is building up his confidence week after week.
"He is improving but we have to give him time."
Vieira continued: "Burnley is not an easy place to go. At the moment we are in a good period, we're creating chances and scored a couple of goals. We have to keep challenging ourselves.
"We want to keep [our momentum] it. It's a really long season and the biggest challenge for us to keep challenging ourselves and to keep improving
"The international break is good as well as the ones who go on international are focusing on qualification and the ones who are here work to go on a different level on the tactical and physical work.
"Its important for us to keep challenging ourselves and to keep demanding from the players. We have the momentum and we have to take care of it and try to do the right things and hopefully it lasts a long time."
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