The two sides are still all square after Thursday's first leg in Germany, but Inter could have broken the deadlock early in the tie as Marcelo Brozovic's penalty was saved by Kevin Trapp.
Brozovic was taking the spot-kick in the continued absence of Mauro Icardi, yet that miss proved to be the Nerazzurri's best chance of an away goal.
Although the stalemate ensures Inter remain in the contest going into the home leg at San Siro, Spalletti was left a little disappointed.
"An excellent result can only be seen at the end [of the tie]," he told Inter TV. "Whether it is the first leg or the second leg, if you do not go through it is not an excellent result.
"We threw away an opportunity. We played in a difficult stadium against difficult opponents who know how to play in Europe, but we were in charge of the game for long stretches."
Despite Brozovic's potentially costly error, Spalletti had no issue with his decision to take the spot-kick, adding to Sky Sports Italia: "Brozovic knows how to take penalties - like [Ivan] Perisic, like [Matteo] Politano.
"But it is always possible to make mistakes. He felt convinced [he could score], but that's OK."
Meanwhile, Lautaro Martinez picked up a booking that will keep him out of the second leg, yet Spalletti still would not entertain talk of Icardi amid a striking selection dilemma.
"I do not want to talk about Icardi - the situation is always the same. There is no more I can add," he said. "I have to think about who is available.
"Even in midfield, players are missing. We are short."