The injury to Joakim Noah did not come up overnight. During the Bulls' 5-game winning streak, you could see that Joakim was not the same. It was becoming increasingly more painful for him to run and jump. Joakim tried to play with the pain, but the Bulls were getting diminishing returns as he tried to stay in the line-up, but was not as effective as he had been most of the season.
The treatment for plantar fasciitis is rest...normally 6 weeks. The Bulls don't have 6 weeks, so the plan is to shut him down through the All-Star Break and then re-evaluate. This injuly affects each player differently and a lot depends on the player's threshold for playing with pain. This injury is especially painful for the Bulls because without Noah on the floor, the Bulls are not a great rebounding team, as you saw in Atlanta on Friday night.
Chris Richard was signed to help out in the front line, but I don't see the Bulls making a trade to replace Joakim. Any trade that is made is going to made will be made with the objective of clearing salary cap room to make the best possible offer to sign a free agent this summer.