The 24-year-old forward has made just three appearances for the Bernabeu club since completing his world-record £86million move from Tottenham in August.
Bale is currently sidelined with a back injury, and earlier this week Madrid denied a newspaper report that the Welshman had suffered a slipped disc and required surgery.
Coleman believes Bale's lack of a proper pre-season is a reason for his injury-troubled start to life at Real, and believes it will take some time for him to produce the sort of barnstorming performances which were his trademark in the Premier League.
"Anyone who plays top level professional football and you don't have a pre-season, if you expect to start any game, you are bonkers, crackers. It doesn't happen," he said.
"If you think you can just pick up where you left off the season before, that doesn't happen either. It takes time.
"It doesn't matter how good you are - and he's a super player and a super athlete. You can't just switch it on or off if you've missed all that pre-season.
"You are always playing catch-up so I wouldn't be surprised if it's after Christmas before we see Gareth getting into it again.
"It may take him some time. He's in a new environment that he needs to get used to and he's playing catch-up all the time.
"I hope it's not serious but it may be some time before we see Gareth doing what he is capable of."
But Coleman dismissed suggestions Bale has been carrying a back injury for some time.
He said: "There's been no problem with his back with Wales - I think he missed the Olympics with his back and our friendly against Mexico that summer. But he's never complained about his back with us."
Coleman also paid tribute to Kelly Breese, who was killed in a car crash on Sunday
The 18-year-old's brother Casey died aged 12 in 2011 after a football goalpost fell on him in Caersws.
The FAW had opened a memorial for Casey last year and his family had attended an international at the invitation of the association.
Coleman said: "We went to open a memorial for Casey last year and recently invited the family down to one of our games, and it was only on the way here to Brussels we were informed of the tragic death of Kelly.
"We had met the family in the summer, a lovely family, and it was devastating enough for them to lose one of their loved ones at such a young age and for this to happen is absolutely awful.
"Our thoughts and prayers are with the family as I'm sure are all those involved in Welsh football."