Muskmelons do not exhibit significant external evidence of ripening because of their hard and thick rinds, increasing the likelihood of purchasing an unripe fruit. In this study, the non-destructive estimation of fruit ripening quality of intact “Honey One” and “Earl’s Talent” muskmelon cultivars was examined. We analyzed the correlation between the major characteristics used for assessing ripening quality (firmness, total soluble solids (TSS), and titratable acidity) and stalk moisture and specific gravity. Moreover, partial least square (PLS) regression analysis was performed for the visible/near-infrared (Vis/NIR) spectroscopy data and reference samples. The correlation coefficients (r) between stalk moisture and flesh firmness were 0.88 and 0.77 for the “Earl’s Talent” and “Honey One” cultivars, respectively. In addition, the specific gravity and flesh firmness of the fruits were negatively correlated; r = -0.65 and r = -0.63 for the “Honey One” and “Earl’s Talent” cultivars, respectively. Moreover, the PLS analysis of the calibration set revealed the determination coefficients (R2) of 0.73 and 0.54 for “Earl’s Talent” and “Honey One”, respectively, for firmness vs. Vis/NIR spectral values. In addition, the PLS analysis of the prediction set showed r2 = 0.51 for “Honey One” and r2 = 0.50 for “Earl’s Talent”. Hence, this study highlighted the possibility of using the status of fruit stalk, specific gravity, and Vis/NIR spectra to predict the ripening quality of muskmelons. However, further studies are necessary to develop more robust non-destructive methods for the estimation of the ripening quality of intact muskmelons.