The Spain international felt that the Blaugrana had done enough to win the first leg in Catalunya, while Marc Bartra is unsure if Gerard Pique will be fit for the return
Diego's barnstorming goal put the Rojiblancos ahead early in the second half, but Neymar curled home a perfect Andres Iniesta pass to deny the visitors victory.
However, despite Barcelona having to come from behind to salvage a draw, Xavi was unhappy with the scoreline, arguing that he and his team-mates had done enough to win the game.
"This isn't a good result," the 34-year-old midfielder told reporters after the game.
"We deserved more, but Diego scored a fantastic goal. Luckily we also scored, so the tie is still open."
The second leg will be held at the Vicente Calderon next Wednesday. Diego Costa is a doubt for the return leg after being forced off a third of the way into the tie with a hamstring injury, while Gerard Pique lasted only 15 minutes before succumbing to a pelvic problem.
"I hope Pique recovers as soon as possible," Marc Bartra, who came off the bench for the centre-back, told reporters. "It's not yet clear if he can play the return game. We hope he can."