Bielsa will send his team out at the Estadio San Mames knowing they will have to overturn a 2-1 first-leg deficit if they are to book an all-Spanish clash with either Atletico Madrid or Valencia in the final in Bucharest on May 9.
He will do so having seen Primera Division rivals Barcelona fail to make the most of home advantage in similar circumstances to lose the chance to retain their Champions League title at the hands of 10-man Chelsea.
Asked whether he needed to have a Plan B in the wake of Barca's failure to break down the Blues' defence, Bielsa acknowledged that football is not an exact science.
He told as.com: "Plan B is not an idea I understand. The game yesterday indicates that the attacking football has nuances. Styles cannot be changed."
Athletic will run out in front of a sell-out home crowd trailing in the tie despite taking the lead through Jon Aurtenetxe's 54th-minute strike at the Estadio Jose Alvalade.
Sporting hit back with goals from Emiliano Insua and Diego Capel inside the final 14 minutes, to give themselves a slim advantage to take to Bilbao.
The Spaniards have faced Portuguese sides seven times in European competition in the past and lost just two, both to tomorrow night's opponents.
However, perhaps significantly, they have won all three of the games they have played on their own pitch, while Sporting are yet to taste victory on Spanish soil in nine attempts Europe, although they have recorded three draws, and a fourth would be enough this time around.
But Bielsa is aware that the tie could yet go to extra time and penalties, saying: "We are prepared."
Sporting coach Ricardo Sa Pinto and his players arrived in Spain two hours later than planned because of adverse weather conditions, and were due to train at the stadium this evening.
But as he arrived in Spain, midfielder Capel admitted he and his team-mates know what lies ahead, telling Abola.pt: "It will be a tricky game."
Bielsa will have midfielder Javi Martinez available after suspension and striker Iker Muniain back from an eye problem, although frontman Oscar de Marcos is banned.
Sa Pinto will be without injured duo Fabian Rinaudo and Alberto Rodriguez, but midfielder Matias Fernandez is fit after a two-game absence.