Karius could probably have done better in dealing with Omer Ali Sahiner's 20th-minute equaliser, the German keeper failing to make what should have been a routine save and conceding his 37th goal of the season in the process.

The 25-year-old was then heckled and jeered by his own fans for the remainder of the game, but there was little he could have done about the second goal when Moryke Fofana exploited the Besiktas defence and chipped the ball over Karius in the 75th minute.

Following the match, Gunes openly criticised Karius for the first time since the keeper joined Besiktas from Liverpool on a two-year loan deal.

He said: "He was at fault for the goals he conceded. Karius has gone a bit stagnant, something is wrong with his electricity, motivation, enthusiasm for the game."

Shinji Kagawa managed to score a last-gasp winner in the third minute of additional time to save his team blushes, but there were rumours in the Turkish press after the game suggesting that Karius wanted to be taken off at half-time due to the treatment he received from the fans.

"It has been like that since the beginning," said Gunes. "He does not really feel a part of the team, it's something we haven't been able to work out and, of course, I am partly to blame for this."

Besiktas have denied reports that Gunes would drop Karius for Tolga Zengin, who is not even a first team player, but the manager made it clear that he would make the move if he could.

"Something is wrong, he has also been unlucky. [He] is talented but it hasn't worked out and we have a problem. Let me put it this way, if I still had Tolga available I would play him."

Besiktas have scored the most goals in the league (50) but have struggled defensively conceding 34 goals -- almost three times as many as leaders Basaksehir (12).

Karius, who has received a mixed reception since making his move from Anfield to Istanbul, has kept five clean sheets in 21 league games this season.