McNamara has missed his club's last three games with a knee injury and will miss both games. Preston North End's Callum Davidson has been called up to replace him.
Davidson will be joined in the squad by the Celtic striker Shaun Maloney, who wins promotion from the Under-21 squad. The Aberdeen goalkeeper Ryan Esson has also been called up in place of the injured Rab Douglas of Leicester. Brian O'Neil of Preston will also miss out through injury.
The Everton striker James McFadden is included in the squad although he will be suspended for the match against Belarus at Hampden Park on 8 October. He will be available again for the trip to Slovenia four days later.
"We need to win both games and have to enter each of the matches with that in mind," Smith said yesterday. "Obviously, Slovenia face a very tough match in Italy and Norway's final game is against Belarus, so we just have to hope they slip up. But all we can do is win our games.
"We find ourselves in a situation we didn't think we would be in," Smith added, "but, if we lose one of our games, then I don't see Norway slipping in two matches. No disrespect to Moldova, but Norway will be favourites to win that one."
However, Smith insists his team have done enough in recent games to deserve a chance of appearing in the play-offs. Italy required a late equaliser from Fabio Grosso to claim a 1-1 draw at Hampden Park before a great display in Oslo earned a 2-1 win over Norway.
Smith said: "None of the other teams outside of Italy have run away with the group, which has helped us. But the main thing is we have helped ourselves. We have played exceptionally well and the players have committed themselves fully."Reuse content