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What you said might happen in this stage of this campaign with them coming back from the international break and getting prepared for the champions league is something that can happen that's dropping points. In as much as Madrid are topping the league with many people thinking or have predicted that Madrid are champions already an upset might happen, like Madrid not only opening a way but dropping more points, starting with there first game after the international break.
They might lose like 3 games or draw them for either Barcelona or Girona to take there spot on the log, it can happen especially when the break is over you see bigger teams messing up, it's expected.
Fatigue will hit on players and when that happens there performance won't be as expected and you'd agree with me that Madrid have so many injury prone players in there first team so if that happens it will affect the team and I even see them being desperate in getting a win in any encounter in the reminder part of the season.
You're right, anything is still possible but I don't think it will be a reality this season. Real Madrid have not dropped points in consecutive matches this season even though they have several injured players. Ancelotti has managed to get the most out of all his players even though sometimes they don't play in their natural positions, but the team's performance so far is good enough not to fail.
Fatigue, player injuries and the accumulation of yellow cards and red cards are disadvantages for any team. But I have no hesitation in saying that Real Madrid will not lose their place at the top of the table until they win it this season. Barcelona and Girona are no longer a threat with Real Madrid leading by a lot of points, so I'll ignore that worst-case scenario for now.