Joseph, a central defender with Premier League club Shooting Stars (3SC), was hit by a stray bullet when gunmen attacked a market in his hometown of Okaki in Bayelsa State.
"Today is a very sad day for us," Rasheed Balogu, 3SC's general manager, told ESPN FC: "This was a young boy with a lot of promise and we are devastated.
"We are still getting confusing reports about what happened exactly but we have been told that the stray bullet came from the JTF [Nigerian Joint Task Force]."
The club's official account tweeted on Monday: "A Shooting STAR is gone! Izu Joseph is gone! Flamboyant defender is gone! RIP, brother. What a life! May God strengthen his family #Tragedy."
Jubril Arowolo, media officer for the club, told sportingtribune.com: "The news came as a shock to us around 11:00 p.m. on Sunday that Izu Joseph was shot by gunmen, though we are yet to get details from the family, hopefully we will make an official statement once we get across to his family later in the day,"
The player, who was home on holiday after the end of the Nigerian football league season, was pronounced dead on arrival at the hospital.