Barcelona coach Hansi Flick criticised the "wrong decision" to disallow Robert Lewandowski's goal for offside as his team were beaten 1-0 at Real Sociedad on Sunday in LaLiga.

Lewandowski thought he had opened the scoring at Anoeta in the 14th minute, but semi-automated offside technology (SAOT), introduced in Spain at the start of the season, ruled the striker's toe was marginally ahead of La Real defender Nayef Aguerd's foot.

The hosts went on to win the game through Sheraldo Becker's strike, ending Barça's seven-game winning streak in all competitions as Flick's team failed to find the net in a game for the first time this season.

"It was the wrong decision, clear," Flick told Barça One after the match. "I saw the picture. It's clear, it's clear, but we have to accept it.

"It was not the referee's fault. At the end of the day, we are humans, we make mistakes, and today was a big mistake."

SAOT is not used universally across Europe. Italy's Serie A was the first major league to implement it and there is a desire to introduce it in the Premier League, but its roll out in England has been delayed as testing continues.

Flick was adamant it failed in Lewandowski's goal, airing his thoughts to the referee at half-time, although he played down the idea he had come across as "angry" in the discussion.

"It was not so angry," he laughed in his post-game news conference. "I said only to him 'It was a goal, it was wrong decision, it was not offside.'

"But it was not his fault. We have to accept it. Until there, with the 1-0 for us, it would be a different match. But at the end, it was different and it was not our day.

"At the end, it's a defeat, but the matches before and after the last break were fantastic. I really appreciate the team and how they are doing."

Barça's second league defeat of the season also came with Lamine Yamal watching from the stands after bruising his ankle in the midweek Champions League victory over Red Star Belgrade.

The 17-year-old, who has six goals and eight assists in 16 appearances this season, did not start the last time Barça lost in LaLiga, either, against Osasuna in September.

"I think it would be an easy answer to say 'OK, we lost because Lamine wasn't there,'" Flick said when asked if it was just a coincidence they have lost both matches the teenager has not started.

"Of course a player like this quality Lamine has, every team will miss it. But at the end, we started good. I think the goal, what I can say it was wrong decision, absolutely, but we have to accept it.

"After the La Real goal we suffered a little bit. I think today was not our day, also in the offence we had not the clear chances to make goals. We made wrong decisions in the last third. We have to accept it today."

Flick added that Barça's and Spain's doctors will now decide whether Yamal joins up with the national team for upcoming fixtures against Denmark and Switzerland in the UEFA Nations League.

The defeat to La Real sees Barça's lead at the top of LaLiga cut to six points, while second-placed Real Madrid also have a game in hand. They return to action after the international break against Celta Vigo on Nov. 23.