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The Blaugrana will have to back up quickly from Friday's (AEDT) 2-1 win on aggregate, progressing to the quarter-finals in the process, with a trip to the Santiago Bernabeu against Real Madrid awaiting.
"Today was an important game, because we are playing for a European trophy," Xavisaid. "We want to go far in this competition, and we are very happy to be in the quarter-finals, as we deserve to be there.
"Yes, we are in good form at the moment heading into El Clasico, but that means nothing.
"I have experienced everything about those games, playing badly and then winning or playing well and then they beat us. Sunday will be a different story, a very difficult and complex one."
Barcelona's win in Istanbul was partly clouded by injuries to Sergino Dest and Gerard Pique, who both had to come off in the second half.
With Barca already leading 2-1, Dest produced a desperate but perfectly-timed sliding tackle on Muhammed Aturkoglu in the 55th minute, injuring his hamstring in the process.
Dest’s injury comes at an inconvenient time for club, with El Clasico awaiting, and country, with Gregg Berhalter announcing Dest in the United States national team’s latest squad only hours after the final whistle.
Gerard Pique was also a second-half substitute, aggravating a groin injury coming into the match and coming off for Clement Lenglet in the 81st minute.
"In the end he told me that it was difficult for him to sprint and we decided to make the change," Xavi said. "We weren’t there to give it away. We only won with one goal, and Pique has had discomfort for a month."
Though Dest's status is questionable, it is as yet unclear whether Pique will be fit in time for Barcelona's clash against their fierce rivals.