The Korean international was involved in a challenge with County midfielder Tom Miller and was stretchered off the field with his leg in a brace.
Manager Owen Coyle revealed that the extent of the injury is not yet known.
"We're still waiting for information from the hospital. Once we have that we will let everyone know what the situation is," Coyle told the Wanderers' official website.
Bolton's Premier League campaign begins on Saturday, August 13 away against newly-promoted Queens Park Rangers.