Team attacked in dressing room before Nigerian match
Two other team members were bruised and bloodied in the attack, they said.
"We were in the dressing room preparing to warm-up when their fans entered and attacked us," Ocean Boys media officer Eddy Ohis said.
Officials said assistant coach Timi Akosubo and defender Anthony Nwodo were in a serious condition. The Premier League game was called off.
The attack was the latest incident in a growing spiral of violence in the professional game in the west African country, which has included attacks on referees by spectators and crowd invasions of pitches in which visiting players are targeted.
There was widespread condemnation of Sunday's incident but the Nigerian Premier League (NPL) said it was waiting for a report before commenting.
Philip Obaji of the 'Football without Violence' campaign said: "Such a situation is unacceptable. This is an attack not only on innocent people but on the image of the NPL and we call for a full investigation and holding those responsible to account."