Christian Mbulu, a defender for League 2 side Morecambe, has died at the age of 23, the club announced on Tuesday afternoon.
No cause of death for the London native was given.
"His loss will be painfully felt by all who had the pleasure of knowing him," the club said in a statement. "The club would ask everyone to respect Christian’s family’s privacy at this sad time."
Mbulu joined Morecambe in January after a short stint with Crewe Alexandra and made one appearance for the club.
Signing his first professional contract at the age of 19 with Millwall in 2015, Mbulu also spent time with Scottish Premiership club Motherwell.
“We are shocked to hear of the news of Christian’s death,” Motherwell chairman Jim McMahon said in a statement. “He was such a friendly, pleasant and dedicated young man who we loved having around Fir Park. Our thoughts are with his family during this incredibly difficult time. We hope their privacy is respected by everyone as they try to come to terms with their loss.”