Multi-user multi-input multi-output (multi-user MIMO) can increase the number of users simultaneously accessing the same base station (BS) without increasing the signal bandwidth. MIMO signal detection which can provide better bit error rate (BER) performance than linear detection with less computational complexity is indispensable in order to enhance the uplink cellular capacity of multi-user MIMO. Maximum likelihood detection (MLD) employing QR decomposition and M algorithm (QRM-MLD) is one of its candidates. It can reduce the complexity of MLD drastically and obtain BER performance close to MLD. QRM-MLD has been widely studied for MIMO spatial multiplexing using orthogonal frequency division multiplexing (OFDM). Recently, it has been reported that QRM-MLD can be applied to the signal detection of single-carrier (SC) transmission in a frequency selective fading channel. In this paper, we introduce the frequency-domain QRM-MLD block signal detection to the SC multi-user MIMO uplink of a cellular system and evaluate the uplink capacity. We show that QRM-MLD can obtain larger uplink cellular capacity compared to the minimum mean square error detection (MMSED) at the cost of the increased computational complexity, but with much less than MLD.