The 28-year-old centre-back picked up the problem during the Blues' 1-1 draw with West Bromwich Albion at The Hawthorns in the Premier League on Tuesday.
The England international suffered the knock during the second half but was not substituted, and he will now undergo more tests to determine the extent of the problem.
"Once I got the knock, I was struggling from then on," he told the London Evening Standard.
"It happened when a West Brom player went for a header and I was on the floor.
"He landed just inside my knee/calf. It is sore and we'll see what it's like today."