The Scots are second-bottom of Group A while their opponents sit three points clear at the top.
Strachan believes that his team will have their work cut out against Marc Wilmots's side at Hampden Park.
"It's a huge challenge because I think they are one of the best international teams in the world right now," Strachan told STV.
"They have terrific players as individuals but they've been together for a long time as a group. It's not a huge group but the players they have in the group are terrific, terrific footballers.
"I think if you look at the Belgians and pick their best eleven and the best eleven of other international teams they are the third most expensive international side in the world on transfer teams. And that was only rating [Christian] Benteke at £8m and I think he's worth a lot more than that now."
Belgium ran out 2-0 winners when the sides last met in October 2012.