A 2-2 draw would put both sides into the quarter-finals even if third-placed Italy beat Ireland and a defeat would probably mean an early flight home.
Spain played sparkling football against Ireland when the recalled Fernando Torres scored twice but the world champions are wary of a dangerous Croatia side who are unlikely to stand around watching Iberian artistry.
In midfield playmaker Luka Modric, heavily linked with a move to Manchester United, and the tournament's joint top scorer with three goals Mario Mandzukic, Croatia have the quality in key areas to cause problems for Spain.
"We watched the two matches they played here and they fully deserve the four points they have," Spain defender Raul Albiol said on Saturday. "Croatia have always had talented players and they are going to make it very tough for us."
Only needing to avoid defeat to reach the last eight, Spain coach Vicente del Bosque will be toying with the decision about whether to retain Torres or revert to the strikerless line-up he put out in the 1-1 opening draw with Italy.
SUIT BOTH
One thing is for sure, according to Albiol, neither side will be worrying about the maths of the group or play for the 2-2 draw that would suit both.
"Of course 2-2 is one of the possible results in football but what is clear is that we will we go out to win," he said.
"There is not going to be any pact and each team will go out there focused on victory so they have their fate in their own hands. There has been a lot of talk [about a pact] but Spain has always gone out there to win and that's what we will do.
"We want the seven points that will win us the group. The team will prepare for the game in the same way as the previous matches conscious of how important it is."
Croatia, who have never played Spain in a competitive game and are unbeaten in open play in their last six European Championship matches, are an intrepid side.
They lost to Turkey on penalties at Euro 2008 and they will be bristling with intent against a Spain side unbeaten in 16 competitive matches.
"They are a grand team, but we have no fear of them," said Mandzukic, who scored the equaliser in a 1-1 draw with Italy and two goals against Ireland. "We're ready to leave our hearts on the pitch, but we will need a little luck, too."
One lucky omen for Croatia is that when they played the holders at the 1996 European Championship they effectively knocked them out with a 3-0 win over Denmark inspired by Davor Suker and his infamous chip over goalkeeper Peter Schmeichel.
The dilemma Croatia, who also have four points, face is that they must go for a win because a 0-0 draw would not be enough if Italy beat Ireland.
The very complicated scenario also means that a 1-1 draw might not be enough for Croatia if Italy beat Ireland by a two-goal margin other than 2-0.
Faced with the harsh prospect of going out with an unbeaten record, Bilic will implore his players to be bold.
