The Croatia international is eagerly anticipating Shakhtar Donetsk's match versus the German champions this week, and expects a difficult encounter
The Ukrainian titans had to settle for a 2-2 draw in the first leg, and Srna realises that they could face a tough task to make it to the quarter-finals of the competition.
"Borussia Dortmund are one of the best teams in the whole of Europe. The first leg was the first competitive game of the year for us, as we'd only played friendlies until then. That wasn't easy. Dortmund have some exceptional players and ruthlessly took advantage of the only two mistakes we made," Srna told Fifa.com.
"We'll have to play even better in Dortmund to stand a chance of reaching the quarter-finals. It'll be a fantastic match in a spectacular setting.
"The stadium will be sold out but it won't be our first time playing against a team with so many fans behind them.
"Dortmund are favourites, but I'd estimate our chances to be around 40 per cent. We'll fight until the last second and give everything because we believe in our ability."
Tuesday's match in Dortmund kicks off at 19:45CET.