According to sources, the UFC is expected to announce Davis' injury and the new UFC 133 main event in the coming hours.
UFC 133 takes place at Wells Fargo Center in Philadelphia.
Davis (9-0) recently defeated Antonio Rogerio Nogueira at UFC Fight Night in March. The win improved his UFC record to 5-0.
Evans (15-1-1) hasn't competed due to various reasons since he beat Quinton "Rampage" Jackson at UFC 114 in May 2010.
The current UFC 133 co-main event features Rich Franklin vs. Antonio Rogerio Nogueira.