"I think we played a bad game, we never got comfortable," Mascherano told Canal Plus. "Apart from creating scoring chances we weren't able to play our style and that's worrisome.
"Our opponents played well and we saw that some of their situations were generated from turnovers and if you want to play for this type of club you have to keep fighting.
"These were two losses [Celta and Real Madrid] in two very different games, but we didn't play well."
Luis Enrique's side turn their attentions toward Europe now, with a visit to Ajax in the Champions League on Wednesday.