**Core Concept**
The unhappy triad is a knee injury that involves three main components: medial collateral ligament (MCL) injury, anterior cruciate ligament (ACL) injury, and medial meniscal tear. This injury is commonly seen in contact sports and is a result of a valgus stress on the knee.

**Why the Correct Answer is Right**
The correct answer is not an injury to the lateral collateral ligament (LCL). The LCL is a ligament that provides stability to the outside of the knee and is not typically involved in the unhappy triad. In contrast, the MCL and ACL are both crucial stabilizers of the knee joint, and injuries to these structures are common in the unhappy triad.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the unhappy triad, as it does not involve the MCL, ACL, or meniscus.
**Option B:** The peroneal nerve is not a structure that is typically involved in the unhappy triad.
**Option C:** The LCL is not a component of the unhappy triad, as explained earlier.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the unhappy triad is a classic example of a knee injury that can be caused by a valgus stress, and it's crucial to assess the MCL, ACL, and meniscus in patients with this type of injury.

**Correct Answer:** C.