The BVB coach is unsure how to compensate for the loss of the Germany internation for his side's crucial Champions League assignment
Germany international Reus has been dogged by fitness woes over recent seasons and was making only his 11th Bundesliga appearance of the campaign when he departed with a thigh problem after 44 minutes of Saturday's 6-2 win over Bayer Leverkusen.
Tuchel acknowledged the setback as a significant blow, stating the 27-year-old was playing at close to his best over recent weeks, and he is still mulling his options as Dortmund aim to overturn a 1-0 first-leg deficit against the Portuguese champions.