Johnson said Wednesday that he was hurt in the first quarter of the Bulls' 90-82 win Monday that tied the first-round series 1-1. Johnson did not practice Wednesday. Game 3 is Thursday in Chicago.
Johnson scored 17 points on 6-of-18 shooting in 39 minutes in Game 2.
"It's sore, but there's no excuse,'' he said Wednesday. "I have to find a way to get through it. It's the part of the season where I can't have this happen. We've fought so hard to get to this point.''
Johnson missed several games during the regular season with a heel injury.
"Mentally, I think I could play if the game was today, but physically, I honestly don't know,'' he said. "We'll have to see.''
Nets interim coach P.J. Carlesimo didn't know about Johnson's injury until he arrived at the practice facility Wednesday morning.
"I'm concerned,'' Carlesimo said. "We'll see how he feels tomorrow. It's unfortunate that things happen like this in playoff time, but injuries are part of the game. Hopefully, he'll be OK. If he's not, then we have some others who can pick him up. We won't have just one player who would have to replace Joe. They all will have to pick it up for him.''