Leverkusen secured the league title with five games remaining thanks to a 5-0 win over Werder Bremen on Sunday, and despite coming into Thursday's second leg with a 2-0 advantage, their concentration is at a maximum.
"We were ready for Sunday after the first leg. We had a clear idea that on Sunday we have a great chance and that we were taking one day in case of winning to enjoy it," Alonso told a press conference.
"But from Tuesday, our focus, our mind, has been on tomorrow's game, on West Ham. We will have enough time after that to reflect.
"But now is the time that we are in Europa league and we have a great opportunity to make it a great season, so far it has been very good but it can get even better."
Earlier, West Ham boss David Moyes joked that he hoped Leverkusen had enjoyed a few big German beers as they celebrated their success.
"A few of them, probably, but not too many," Alonso said.
"We had some control to get ready for tomorrow and for sure it was a moment to enjoy it, but we have talked enough about what happened, about the celebrations, now let's talk about what's coming tomorrow and West Ham."
Alonso is expecting a typical European night in London, and is well aware of the type of atmosphere his side can expect.
"Once you come to England, you know that the English supporters, the West Ham fans they will push for them. We will have an electrifying atmosphere, it's quarter-finals, a great chance, Europe," he said.
"So we have all the ingredients to have a special night and hopefully we will be ready and I have a good feeling about the team."
Leverkusen are on a 43-game unbeaten run in all competitions and the manager sees no reason why his side will stop now.
"Until this moment, the team, the players they have given me no reasons to doubt them," Alonso said.
"Because of the commitment, because of the concentration, the mentality they have had, so I have no reasons to have doubts about tomorrow even after a big success."
