Joakim Noah will miss the next 30 or so games recovering from surgery and with the loss, Bulls fans immediately start digging for replacements and discussing trades.
Replacements simply aren't going to be found outside of the existing roster though. Most teams play no more than a nine man rotation with four to six players on the bench in case of emergencies, development, and other such problems.
As such, in the vast majority of cases, the talent of players not in the league is considerably beneath the talent required to play in the league. The next best 150-200 players that aren't in NBA rotations are sitting on the bench of other NBA teams. If your bench isn't stacked with some of those guys, then your odds of catching lightning in a bottle with a D-League call up or unsigned player are minimal.
If signing someone isn't the answer, then how about trades? Prior to the injury the Bulls were looking to bring in a SG, and they'd have dealt from the bigs to do so. However, now the Bulls have no extra depth in the front court to trade for a SG, but they also have no guards to move to trade for a big man.
Due to the Bulls off-season plan of acquiring players this year, they also don't have any expiring contracts to deal in an attempt to match salary. Would Portland give up on Marcus Camby for an expiring and a 1st? Perhaps, but we don't have the expiring to match. Same thing applies for Joel Przybilla.
The answer isn't going to come through trades, because we simply don't have the salary matching to just use a draft pick, and we don't have the depth to trade from present players.
As such, the answer will come from the existing roster. The Bulls will play Taj Gibson 36+ minutes a night, Omer Asik will get a bump in playing time, and the Bulls will go small more frequently. On top of that, one of Thomas, Johnson, or Scalabrine will likely get a shot to take on 15 minutes a night of fairly regular action.
If the Bulls were to add someone, it'd simply be to have another body to bang against in practice. However, even that scenario has limited value as the bulls still have Boozer, Gibson, Asik, Scalabrine, Johnson, and Thomas who can man those positions in practice.
Unless there's another injury, look for the Bulls to just toe the line with the present roster.