The Brazilian playmaker was stretchered off the pitch around the half-hour mark of the Reds' 2-0 victory over Sunderland at Anfield on Saturday afternoon.
Coutinho, who has scored six goals in all competitions so far this season, winced in pain after he and Didier Ndong caught one another's feet while tussling for the ball in the final third.
The 24-year-old is due to undergo a scan today to learn the extent of the problem, with some reports claiming that Liverpool will be without their influential player for the rest of 2016.
On Instagram, Coutinho wrote: "I'd like to thank my family, fans and friends for all the positive messages, that's very important to me."
Liverpool currently sit second in the Premier League table, one point behind Chelsea after 13 games.