Bale joined Spanish giants Real from Tottenham Hotspur last week in a deal widely reported to be the world's most expensive transfer at around €100m.
But Bale was an unused substitute for his country's 2-1 loss to Macedonia in Skopje on Friday and Wales manager Chris Coleman revealed on Monday that the winger was left on the sidelines because of a groin injury suffered in training.
"We had a conversation with Gareth before the game, he had a tight groin from the day before and we could not take that chance," Coleman said. "As we speak he has gone to have another scan on it to clear his mind so he knows everything is alright."
Bale has not played since mid-July due to a foot problem and his latest injury concern comes just days before he is scheduled to make his Spanish La Liga debut with Madrid at Villarreal this weekend.
Coleman admitted the 24-year-old suffered the problem during Wales's training session at the Philip II Arena on Thursday. But he is still hopeful the results of the scan will allow Bale to play some part against Serbia in Cardiff on Tuesday.
"We went into the Macedonia game with everything great," Coleman said. "Gareth gets his move to Real Madrid, everything is positive. Then Gareth picks up a strain in training and can't play in the game which is disappointing.
"He was never going to be available to start either of these games but at best he would have come on for maybe half an hour. There is a small chance of that tomorrow night, we will see when we get the scan results back and how he feels."