Bale - the world's most expensive footballer - missed Real Madrid's UEFA Champions League match against FC Copenhagen on Wednesday night because of a thigh injury.
Real coach Carlo Ancelotti had already revealed Bale would need "15 days" of rest - something confirmed by Wales boss Chris Coleman who said the forward had been included before he learned of the full extent of the injury.
Coleman told Sky Sports News: "Sometimes you get the (medical) report from clubs to say that players have problems - but we want the chance to work with players and if they've got a chance and there's a small window that they can play some part then we want to affect that.
"Speaking to our doctor yesterday - after we'd released the squads to clubs at the start of the week - the report from Madrid is that it's more serious and at least two weeks.
"That doesn't really give us any chance to work with him without there being a major risk of worsening the injury or even causing a new one.
"Something positive may happen and there may be an improvement but looking at the statistics for that particular injury and the medical report it will be at least two weeks."
Captain Ashley Williams is also included despite being a doubt due to the ankle ligament injury which has kept him out of Swansea's last three games.
Swansea boss Michael Laudrup has asked Coleman not to play Williams - although he was happy for the defender to join up with the squad.
Coleman added: "Ash is as important to us. Ash knows his body and if he misses it's because he needs to. It has to be down to the player. If he is at any risk he won't play.
"I expect Michael to look after Swansea, we look after Wales."
Wales squad: Myhill, Hennessey, Fon Williams, B Davies, Gabbidon, Gunter, Matthews, Ricketts, Taylor, A Williams, Allen, Collision, John, King, Ledley, Ramsey, Vaughan, Bale, Bellamy, Church, Robson-Kanu, Vokes.
You can see both of Wales' qualifiers live on Sky Sports - Wales v Macedonia is on Sky Sports 3HD at 7.30pm on Friday October 11 with their trip to Belgium on the same channel on October 15 at 8pm