The Welshman attempted to carry on after going down in what seemed considerable pain.
However, just minutes later he sat back down on the turf and asked to be replaced, with Zinedine Zidane bringing on Marco Asensio.
Bale sported a concerned look on his face as he was withdrawn and could be a doubt for Saturday’s La Liga clash with Sporting Gijon and El Clasico a week later.
Zidane said after the match:
“Gareth Bale suffered more of an ankle twist than a knock, but we will have to wait and see what the problem is.
“Tomorrow he will be examined by our medical staff and after that we will find out (more).”
He left the game very much in the balance, and it took substitute Karim Benzema to head a late winner for the holders to secure their place in the knockout stages.
A draw would have been enough to send the in-form La Liga leaders through from Group F alongside Borussia Dortmund, who beat Legia Warsaw 8-4.
It appeared Zidane’s side would be left with just that after a penalty from Adrien Silva after 81 minutes had cancelled out Raphael Varane’s first-half opener, with the home side having seen defender Joao Pereira sent off after appearing to punch Mateo Kovacic.
However, with just three minutes left, Benzema nodded in a weighted cross from Sergio Ramos to secure victory and set up a Madrid showdown with Dortmund for top spot next month.