AVB admits he will have to cut one of his centre-backs loose at the end of the season, with Gallas the most likely candidate to leave given that his contract expires in June - two months before he turns 36.
"We won't start another season with five (centre-backs), for sure," Villas-Boas said.
"It's a difficult one. We have five top central defenders at the moment - a mixture of young players coming through with lots of experience, and then you have such tremendous central defenders as William, Dawson and Younes Kaboul.
"William has been a massive player for us this season. He's a player we trust a lot. Whatever we decide regarding his future, we'll have to wait and see, but we are aware of what a presence he's been for us this season."