Looking to cut costs and needing to pay huge salaries to guys like Rudy Gay led the Grizzlies to decline offering O.J. Mayo a qualifying offer. That means he'll become an unrestricted free agent on July 1st. Are the Celtics interested? You would have to assume so.
Green Street " Grizzlies to make OJ Mayo an unrestricted free agent
Mayo immediately becomes a target for the Celtics, who are looking to add some scoring punch to a bench that was one of the worst offensive units in the league. The C’s expressed their interest in Mayo at the trade deadline in a deal involving Ray Allen, but they weren’t able to complete the trade. He will be among a group of unrestricted free agent five scoring guards that includes: Ray Allen Jason Terry, Lou Williams and Jamal Crawford.
How much they'll have to spend to get him and what he'll be looking to get are several layers of complicated, but Paul Flannery does his usual excellent job in the link above. My personal guess is that he'll want more than we want to give him, but time will tell.
Jamal Crawford is another guy that was involved in Celtics trade rumors before he opted to become a free agent as well.