The Russian outfit meet Jurgen Klopp's men at Stadion Petrovskij on Tuesday in the first leg of a UEFA Champions League last 16 tie.
Due to Russia's mid-season break, Zenit - who top their domestic league - have not played a competitive fixture since losing 4-1 to Austria Vienna on December 11 during the Champions League group stages.
Head coach Spalletti insists his players are nevertheless fully prepared, but recognises the quality of Dortmund, last season's runners-up, may prove significant.
"Dortmund are a very strong team who last year played in the Champions League final," he said.
"That says a lot. In the Bundesliga there is one team out in front: Bayern Munchen. Dortmund are fighting for second place in the Bundesliga, one of the strongest European leagues.
"We're going to play one of the strongest opponents that we can possibly imagine. I don't know if our 100 per cent readiness is enough for us to reach Dortmund's level. But we're going to be 100 per cent ready."
The Italian believes Zenit can continue to grow in stature and eventually challenge in Europe's premier competition, adding: "The Champions League commands a lot of effort and attention and can affect the preceding game or the one that follows.
"We are working to keep pace and, in time, grow and improve. Behind us we have a big city and a huge number of fans who care about the club.
"The Zenit management are very ambitious people. They set high goals and we strive to meet them. I've told my players that we have a rare opportunity to not just write a chapter in our history, but put the title on the cover story of Zenit."
Thank you for reading 5 articles this month* Join now for unlimited access
Enjoy your first month for just £1 / $1 / €1
*Read 5 free articles per month without a subscription
Join now for unlimited access
Try first month for just £1 / $1 / €1