The Catalan outfit laboured to a 1-1 draw with Rayo Vallecano on Saturday afternoon, with an own goal from Floriane Lejeune cancelling out an opener from Unai Lopez in the 39th minute.
Barcelona are now three points behind league leaders Girona, who have a game in hand, in the La Liga table, and they have only managed to win two of their last five matches.
Xavi's position as head coach has been called into question in recent weeks due to some poor performances, and the club's legendary midfielder has admitted that his side must improve, but he said that some key decisions went against the visitors on Saturday.
"I think there were two halves; in the first we dominated but we didn't go for the game. In the second half we did what we wanted: dominate and create chances, and we scored a goal," he told reporters during his post-match press conference.
"Starting matches by losing? This has happened many times this season and it is difficult to come back. We have to improve that. We must criticise ourselves and improve. We have to get very close to what we have been in the second half.
"On the first goal, I spoke with the flag referee. He told me that there was doubt, but in the end they awarded the goal. These are difficult situations going against us.
"There is also a penalty following a foul on Raphinha, but we should not stop there. With our level in the first half, it is time for self-criticism.
"We are having trouble with referee decisions that are interpretable, we are not having any luck so far this season... Always having trouble.
"In the first half we lacked the mentality of going for the game. If we want to win titles this season we have to change that mentality. The second half was good but it wasn't enough, we woke up late."
"Then I'm told I'm looking for excuses, but the foul on Raphinha is a clear penalty. It happened to us in Getafe, in Granada and today. We lost because we weren't good in the first half, and that's no excuse, but it's a clear penalty.
"The team's mentality must change. We must go to win from the first minute. We can turn the situation around. There is still time."
Frenkie de Jong made his return against Rayo, playing the full 90 minutes after recovering from an ankle issue, but there was no Marc-Andre ter Stegen, with Inaki Pena making his first appearance of the campaign between the sticks.