Mauricio Pochettino admits Tottenham fluffed their first attempt at the Champions League under him last season but insists there will be no excuses second time round. Spurs host Borussia Dortmund at Wembley on Wednesday as they look to learn from the mistakes of a disappointing opening campaign under Pochettino at Europe's top table.After failing to progress from a relatively kind group that featured CSKA Moscow, Leverkusen and Monaco, Pochettino reflected his squad had struggled to cope with the physical and mental demands of the Champions League.They are one season wiser this year but have also been handed a far tougher draw that, as well as Dortmund, includes reigning champions Real Madrid in Group H.Cypriot side APOEL complete the line-up and it may be that Tottenham's best chance of qualification is to beat Dortmund to second place. They cannot afford another slow start like 12 months ago."Last season was our first experience of the Champions League - previously we play Europa League, for 98, 99 per cent of the players, and for myself too," Pochettino said."That experience [of last season] is important. We know very well what the competition demands from you, and I think that is so important."It was a very painful experience because we could not be at the level we should have been but today, it's not an excuse. We know that tomorrow will be very tough. We need to be ready to compete at a higher level."Pochettino is also finding his feet in the Champions League. He chopped and changed his tactics throughout last year's tournament and only settled on his current formation of choice, 3-4-2-1, after Spurs' hopes of qualification were over.The Argentinian, however, has successfully cemented Tottenham among the Premier League's elite and now he has Europe's super clubs in his sights."Remember me, three years ago I said we needed to reduce the gap with the big sides and three years after we are fighting to win the Premier League," Pochettino said."Why not now start again to create the same in the Champions League and try to reduce the gap with these clubs?"They are at a completely different level and philosophy but I think this season will be a very good opportunity to challenge them and see our reality."Tottenham will have to overcome their jinx at Wembley, where they have won only twice in their last 12 fixtures, and also do without Dele Alli for the first half of the group stage.The midfielder is serving a three-match ban for a red card picked up against Gent in February and his absence puts even more emphasis on Harry Kane, who opened his league account with a double against Everton on Saturday."I have said before I want to break into that world-class bracket and to do that you have to play well in the Champions League," Kane said."The Champions League is a big stage, all the best players in Europe, if not the world are here, and to be the best you have to produce your best against the best. I have six group games to prove that."Danny Rose and Victor Wanyama are both out with knee injuries but right-back Serge Aurier is set to make his debut in place of Kieran Trippier.Erik Lamela and Georges-KÃ©vin N'Koudou have begun light training following hip and foot injuries respectively but neither is ready for a return to competitive action.