South Africa host the Pharaohs on March 26 at Ellis Park in a crucial game in Group G.
International ace Pienaar has been nursing a groin injury, which he sustained a month ago, and it's still unclear whether or not he will be able to feature in the anticipated clash.
His absence would be a severe blow for the home side, Mosimane believes.
"It is a concern, because he is an important member of the team. Yes it is a concern … we need his contribution and leadership as captain," said Mosimane.
"We need his experience from playing in the Confederations Cup, World Cup and more recently in the UEFA Champions League, playing away at San Siro against AC Milan."
South Africa doctor Ephraim Nematswerani allied fears over Pienaar's problem, saying the 29-year-old is most likely to be fit for the game.
"When all players arrive they are assessed and a decision will be made whether they stay in camp and if they are not fit to stay in camp, they are ruled out," he stated.
"In this case, we made an assessment and the player is staying on in camp, because we are satisfied that his injury is mild and he will start training on Wednesday."
African champions Egypt, who are languishing at the bottom of Group G on one point, need to beat leaders South Africa in order to revive their qualification hopes.