The teachings relate to a method 100 performed in a network node 2 for determining a link adaptation parameter, SINRLA,i, for a wireless device 3. The network node 2 supporting a multi-antenna transmission mode comprising spatial multiplexing layers for transmission of data on a channel between the wireless device 3 and the network node 2. The method 100 comprises: determining 110 a channel covariance matrix H HH for the channel, wherein H is the channel matrix for the channel; approximating 120 a post-equalizer signal to interference plus noise ratio SINRapprox., for a spatial multiplexing layer i using the channel covariance matrix H HH; determining 130 an offset SINRoffset, i to be the difference between a received signal to interference plus noise ratio SINRreceived and the approximated post-equalizer signal to interference plus noise ration SINRapprox.,i, and determining 140 the link adaptation parameter SINRLA,i to be the approximated post-equalizer signal to interference plus noise ratio SINRapprox.,i compensated by the determined offset SINRoffset. Corresponding network node, computer program and computer program products are also provided.