The linebacker, who made 62 tackles in 2012, joined the Super Bowl champions last month after being cut by the Oakland Raiders.
DeCosta told the Baltimore Sun: "I think this about McClain, he deserves a second chance.
"If you asked him, he would probably admit to making some mistakes. We think he warrants a second chance."
The 23-year-old has been the subject of numerous off-field matters, and currently faces two pending cases regarding driving charges.