This paper evaluates a low-complexity Multiuser Adaptive Modulation (MAM) scheme for an uplink massive multiple-input and multiple-output (MIMO) systems with maximum-ratio combining (MRC) linear receivers, which requires only slow-varying large-scale shadowing information for the users. For a channel that includes both small-scale and large-scale fading, the probability density function of signal-to-interference-plus-noise ratio (SINR) is mathematically analyzed and verified by simulation. Furthermore, closed-form expressions are derived for the average spectral efficiency and bit error outage. Since the MRC is desirable in low transmit power, the obtained analytical expressions are approximated at low power levels. Moreover, the paper investigates different users’ arrangements around the base station to achieve the maximum possible bit rate. For MAM with joint power control, optimal power adaptation strategy switching thresholds are also acquired. Compared to the existing research literature, the proposed adaptive scheme by the MRC receiver gives similar performance as a proper adaptive method at low power transmission.