The players suffered the knocks during a training session at Hampden on Thursday morning but Strachan would not elaborate on their identities or the nature of the injuries.
He said: "We were practising set-plays this morning and they really got into it. So I've got a couple of injuries after that."
Goalkeeper Allan McGregor - who would have been suspended for the Belgium game but available for next week's visit to Macedonia - then also withdrew through injury. David Marshall is tipped to be handed the gloves in McGregor's absence, with Matt Gilks and Craig Samson also in the squad.
Strachan has decided who will feature between the sticks against the Belgians but declined to reveal his selection just yet.
He said: "I've not told him yet so I would rather tell him than having him hear it on the news."
Belgium arrived in Glasgow sitting top of the group, while Scotland's qualification hopes have been over for some time.
Strachan said: "If the belief in ourselves is the same as it has been in the last couple of games, it's a challenge, but it's a challenge that can be overcome.
"It's a huge challenge because I think they are one of the best international teams in the world right now.
"They have terrific players as individuals but they have been together for a long time as a group.
"It's not a huge group but the players they have in the group, the regulars, are terrific footballers."