Croatia have the unenviable task of trying to halt the rampaging Roja, who hammered Ireland 4-0 at Arena Gdansk on Thursday with Fernando Torres scoring twice as the world champions hit top gear.
A shock win over Spain will see Croatia qualify for the quarter-finals as group winners, while a draw could be enough depending on whether Italy beat Ireland in Poznan, Poland.
For Spain, the task is straight-forward: a draw means qualification and a win ensures first place. Spanish confidence is high after their star-studded forwards battered the Irish using their 66 percent of ball possession to produce 26 shots on goal, 20 of which were on target, and underdogs Croatia have their work cut out.
Bilic has admitted his players will need to produce something special to make the champions dance to Croatia's tune, but his team showed plenty of pluck to hold Italy on Thursday in Poznan. "What I can say is that we will need to play the best game of our lives," Bilic said.
"We drew 1-1 against Italy, one of the best teams in the world. "We are still in a realistic position to go through and we have a chance. We need to remain confident. "Spain will enjoy more possession, but they won't control the ball the whole time and we'll also have chances.
"I hope luck will be on our side too," added the 43-year-old, who steps down after the tournament to take over at Russian side Lokomotiv Moscow.