The 25-year-old, who was called up as injury cover for the Lions' successful tour to Australia last summer, took a blow to his ankle injury as Gloucester secured a 38-30 win over London Irish.
The extent of the injury is due to be known soon but Gloucester director of rugby Davies did hint at a concern that the centre might be out for a significant period of time.
"We all know how committed Billy is as a player and for him to come off , especially in this game with a lot of emotion going on, says a lot but we will have to wait and see," said Davies.
"It's an ankle problem but with all of these things it's very difficult to give a formal assessment. We will monitor the situation over the next 48-hours and in that period we will have a scan to determine the amount of damage.
"It's not great for him but until we have a clearer picture we can't say how serious it is."