"We are expecting a tough game for sure. West Ham have the experience after their win over (SC) Freiburg in the round of 16, where they came from behind to get a good result," Alonso said, at his pre-match press conference on Wednesday evening.
"West Ham have good players, and they have done well in Europe over recent years, which we have really thought about and prepared for, so we will need to have our best performance tomorrow.
We are ready to have an intense game and have another game similar to last week. We are not coming here to defend the result, we will play to win the game and that is the best approach for tomorrow.
When you come to England you know the West Ham fans will push for their side (to win) and it will be an electrifying atmosphere. We can't wait to get going again."
Now Bundesliga title winners, Bayer are still hunting two more trophies.
Alonso added: "We have a great opportunity to make a great season even better. It's a quarter-final in Europe, so we have all the ingredients to have a special night.
"We were ready for Sunday after the first leg and had a clear idea that we had a great chance (to win the title) and were prepared to take a day off (on Monday) to enjoy it.
"But from Tuesday, our mind and our focus has been on tomorrow's game and West Ham.
"I feel the hunger and desire of these players to keep going and not to stop. We have a big challenge tomorrow, but we are going to be ready, and if we don't go through it isn't going to be because we didn't have the mentality, it will be because of the way the football happened.
"We are confident, but in a very humble way. We have the experience from last year of reaching the semi-finals, and we want to go even further this year.
Hopefully we can reach the semi-finals. It will come in a very intense May schedule, but it is so good to be at this stage of the season fighting for everything."