Morecambe defender Christian Mbulu died on Tuesday afternoon, aged 23.
The former Millwall player joined the Shrimps in January following his release from Crewe Alexandra and the League Two club paid tribute to him.
'Christian proved to be an extremely popular member of the squad,' a Morecambe statement read.
'The news of his sudden and untimely passing has been a shock to us all.
'His loss will be painfully felt by all who had the pleasure of knowing him.'
Motherwell chairman Jim McMahon added: 'We are shocked to hear of the news of Christian's death.
'He was such a friendly, pleasant young man who we loved having around Fir Park.
'Our thoughts are with his family during this incredibly difficult time.'