Atleti is already guaranteed Champions League football after Christmas and is expected to rest a number of key players in St Petersburg.
However, Spalletti feels a weakened opponent might not necessarily play into Zenit's hands.
"I would prefer it if Atletico played their full-strength side because the absence of several players for the opposition would be a loss for us," Spalletti said at a press conference.
"I see a danger in the fact that my players might think that such an Atletico side is weaker but this is not the case."
Spalletti then went on to stress that the home side will be without a number of first-team regulars as well, with Danny as perhaps the biggest name missing out.