Schalke 04's training camp in Türkiye ahead of next week's Bundesliga restart did little to prop up their confidence with the last-placed club having failed to win any of their five friendly matches so far.  Their 1-0 loss to Nuremberg on Tuesday ahead of Wednesday's return to Germany had been preceded by four other failed attempts for a win: 2-2 draws against Zurich, Rapid Vienna and third tier club Osnabrueck and defeat by Hajduk Split.   "I keep saying that we need to be making fewer mistakes," Schalke coach Thomas Reis said following Tuesday's loss. "But then it is again a mistake from a young player that leads to the goal (for Nuremberg)."  "We just cannot present ourselves like that," he added.  For player Kenan Karaman it is inexplicable why Schalke's form can fluctuate wildly during a single game.  "Two different halves. That just cannot happen. I am furious and I include myself in this," said the forward.   "We change 11 players and then we show a different face even though we train hard here, know the plays and the game plan. We then make a stupid mistake and we are not clever enough in defense."   Schalke won promotion last season following their shock relegation a year earlier but they have struggled with life in the top tier, having won just two of their 15 league matches.   They have one last friendly match against Werder Bremen in three days before the Bundesliga resumes next week with Schalke travelling to Champions League club Eintracht Frankfurt.