"I have warned the players that, while Liechtenstein are undoubtedly an inferior side to us, every team we play these days is so motivated," he said in a press conference today.
"They are a well-organised side and they caused problems for Lithuania [in a 0-0 draw on Friday]. Against Lithuania they drew and played well, so we are expecting a difficult game.
"If we play to the best of our abilities then we should be fine, but we will make sure that we are fully prepared for whatever threat they might pose."
Del Bosque admitted that Liechtenstein, who lost 4-0 when the sides clashed in Vaduz 12 months ago, are likely to park the bus at the back, leaving the onus on the hosts to try and find a way through.
"We will have to be patient and precise, look for the one-on-ones, the one-twos and use all our strengths," he added, before admitting that changes to the team that beat Chile 3-2 in a friendly in Switzerland on Friday are likely.
"We will make one change in every area of our team; at the back, in midfield, and up front," he said.
Spain have won all five games so far in qualifying group I and three points at the Las Gaunas Stadium will give them an unassailable lead from the second-placed Czech Republic with two matches to spare.