* Bale to have scan on left thigh
* Could make home debut in city derby on Saturday (Recasts after game with Ancelotti quotes)
MADRID, Sept 22 (Reuters) - Gareth Bale was forced to wait for his Bernabeu debut after suffering a muscle problem in the warm up to play Getafe on Sunday but Real Madrid coach Carlo Ancelotti said the injury was not serious.
The world's most expensive player, who cost Real around 100 million euros ($135 million) when he was signed from Tottenham Hotspur three weeks ago, has made two appearances so far away at Villarreal, where he scored, and at Galatasaray in the Champions League.
Real medical staff could be seen attending to Bale's left thigh as the sides warmed up for their La Liga match and soon afterwards Isco was named in the starting 11 in his place with Raphael Varane on the bench.
An official club statement said Bale had felt a pain in his thigh and that he had dropped out as a precaution.
"Bale had a small problem during the warm up," Italian Ancelotti told a news conference after Cristiano Ronaldo scored twice in Real's 4-1 triumph.
"After speaking to the doctors I don't think it is anything serious, but we will have to wait until Monday when they will do a scan.
"The player wasn't comfortable and we preferred not to take any risks. He isn't very pleased because he was very excited about playing at the Bernabeu."
There had been great expectation among home fans to see Bale play in a Real shirt at the Bernabeu for the first time, on a day local newspaper Marca had dubbed 'B-Day'.
Real's next game is away at promoted Elche in La Liga on Wednesday, and on Sunday they have a city derby at home to joint-leaders Atletico Madrid, who have made a perfect start to the season.
Diego Simeone's side are two points ahead of Real, who are in third.
"I don't know how much time he will be out of action, we will see what happens tomorrow but I am sure he will be ready for next Saturday," Ancelotti added.
"It could be to do with his unusual pre-season which has been unusual in physical and psychological terms. We are working hard to get him into peak condition."
Bale missed the pre-season with his former club Spurs as he suffered a couple of minor injury problems, while there was extensive media coverage of the lengthy transfer negotiations between the two clubs before a deal was finally reached on Sept.1.
$1 = 0.7402 euros Reporting by Mark Elkington; Editing by Rex Gowar