Bale was named in the starting XI for Madrid's clash at home to city rival Getafe, but pulled up with an injury as he took a shot in the warm up and was replaced in the side by Isco. The former Malaga man was on target, along with Cristiano Ronaldo (twice) and Pepe in a 4-1 victory.
Bale scored on his Madrid debut in the 2-2 draw at Villarreal and came off the bench to impress in Real's 6-1 win at Galatasaray on Tuesday, but the 24-year-old has yet to feature at the Santiago Bernabeu after making his 100 million euro move from Tottenham earlier this month.
"Bale has a small problem," coach Carlo Ancelotti told the media after Madrid beat Getafe 4-1 on Sunday. "We can't say if it is an injury, we will have to wait until tomorrow to know more.
"He had a strange preseason, both mentally and physically. He had to wait a long time [for the move to be completed] and that is a problem."
Bale is now a big doubt for Madrid's trip to promoted side Elche in La Liga on Wednesday, but looks likely to make his home debut next Saturday in the capital clash against Atletico at the Santiago Bernabeu.
"I don't know if he will be back for Elche," Ancelotti explained. "But I am sure he will be ready to play against Atletico on Saturday."