Rangers may be missing striker Kris Boyd for their Champions League qualifier against FK Zeta after limping off during yesterday's 3-0 victory over Inverness Caley in their opening SPL match of the new season.
A double from Barry Ferguson and a strike from Nacho Novo secured all three points in the Clydesdale Bank Premier League opener against a team Rangers lost to twice last season.
Rangers now prepare to travel to Montenegro, where they hope to book a European clash with Red Star Belgrade or Levadia Tallin in the third round of qualifying, having scraped an unconvincing 2-0 win from the first leg at Ibrox.
But Smith fears they may have to make the trip without star striker Boyd after he suffered an ankle injury during the clash at the Caledonian Stadium.
"He was injured and couldn't carry on," said the Rangers boss. "It's too early to say if he will be fit for Tuesday's game. He's a doubt at the moment."