Kenny Miller is the major doubt for the Group I game in Alicante as he struggles with a groin injury that sidelined him for the 1-0 win against Liechtenstein.
''Where to start?'' said Levein when asked about the injury situation on Monday. ''The most doubtful will be Kenny. He hasn't improved from Friday until today. I'm not definitely ruling him out but he would be the most doubtful.''
Craig Mackail-Smith, who scored the winner against Liechtenstein, has a back problem, captain Darren Fletcher has an ankle knock and winger Barry Bannan has a gash on his heel.
''I am more hopeful with (Mackail-Smith and Fletcher) than Kenny but as yet I can't give any definitive answer,'' Levein said. ''Barry will do a little bit today. His problem is whether he can get his boot on so it doesn't open up the injury again, it is in an awkward place. The doctor had to put some glue on it to hold it together.''
Against Spain, Scotland must at least match Czech Republic's result at Lithuania to make the playoffs.
''It's going to be a difficult match and we will probably be defending for the majority of the match,'' Levein said. ''I have no doubt that the defenders will need to be our best players and our goalkeeper will need to be on top of his game but ultimately we need to make chances and score goals, or a goal.''
Spain has dominated the group with seven consecutive victories and is going for its 14th straight win in competitive fixtures.
The world and European champion's last tournament defeat came in the first match of the 2010 World Cup - a 1-0 reverse against Switzerland. That was only a passing hiccup - Spain won its next six matches to lift the cup for the first time.
Del Bosque says he will rotate his squad against Scotland, with Valencia left back Jordi Alba expected to make his debut and goalkeeper Iker Casillas rested in favor of either Jose Reina or Victor Valdes.
Real Madrid defender Raul Albiol is definitely out after breaking his cheekbone in training Sunday.
Athletic Bilbao's Javi Martinez is an option in defense, while Thiago, Pedro and Santi Cazorla could all start.
Czech Republic trails Scotland by a point and will secure a playoff spot with a draw at Lithuania if Scotland loses to Spain.
''It's clear that if Scotland wins (at Spain), they will advance. But I don't think that's going to happen,'' said captain Tomas Rosicky. ''And we will win in Lithuania. We have to win and that's our goal.''
Bordeaux midfielder Jaroslav Plasil will be back in contention after returning from suspension, but Tomas Hubschman misses out after receiving a red card against Spain on Friday.