Splenic infarction, being one of the rare and serious complications of infectious mononucleosis, occurs due to splenomegaly and local vascular congestion, sometimes accompanied by transient hypercoagulability. However, it is usually not the presenting complaint. We present the case of a 24-year-old obese male with a past medical history of sleep apnea who presented to our ED with a complaint of moderate to severe left upper quadrant pain. His abdominal pain had continued intermittently for two weeks and progressively worsened, prompting him to come to the hospital. Left upper quadrant tenderness was noted during the physical examination. CT scan of the abdomen and pelvis with contrast revealed moderate splenomegaly and multiple hypodense lesions in the spleen consistent with infarcts. The infectious mononucleosis screen and serological tests for Epstein-Barr virus were positive. However, the patient lacked classic symptoms of infectious mononucleosis. Diagnosis of infectious mononucleosis-associated splenic infarction was made, and the patient was started on conservative management in the hospital. The patient was discharged after five days without complications and was advised to avoid contact sports and strenuous activity for at least four weeks. This case illustrates that splenic infarction can be a presenting symptom in otherwise missed infectious mononucleosis infection and highlights the importance of an elaborate history, examination, and laboratory workup.