The meniscus is one of the most important structures of the knee that needs to be saved if possible. Previous studies showed that increasing time from an anterior cruciate ligament (ACL) injury (TFI) could lead to a meniscal tear, especially medial meniscus (MM). We developed the present study to see if the TFI alone is a predictor of meniscal injury in ACL-deficient knees. We included 111 patients who had a reconstructed ACL injury at our institution from March 2015 to March 2016 in this retrospective cohort study. All demographic data, including age, gender, and body mass index (BMI), were collected. We also recorded the mechanism of injury and the TFI. We extracted the meniscal condition at the time of surgery from the surgical report. All patients were followed up for a mean of 23 months, and the Lysholm score and pain visual analog scale (VAS) score were obtained. The mean TFI of patients with MM tear was 17.4 ± 16.8 months, which was significant than the patients with lateral meniscal (LM) tear (9.3 ± 8.3 months) and intact meniscus (7.4 ± 8.1 months) (p = 0.001). Patients with TFI less than 6 months had a significantly lower rate of MM tear, and increasing TFI more than 6 months could increase the rate of MM tear (p = 0.001). We could not find any association between age, BMI, and gender and meniscal injury. At the latest follow-up, Lysholm and VAS scores in patients with and without meniscal tear were the same. Our study confirms that increasing time from the ACL injury would increase the risk of MM damage. The cutoff point for this risk factor is 6 months from initial injury; therefore, to save the meniscus, it might be better to perform ACL reconstruction within 6 months in ACL-deficient knees.