O'Driscoll's Lions career is over after he was dropped by head coach Warren Gatland in favour of the all-Wales duo of Jamie Roberts and Jonathan Davies for the third and final Test.
"We'd anticipated that Brian would be there, but we haven't spent the time and consideration that the Lions staff will on the matter," Deans said.
"It would have been a great sign off for Brian because he's a legend of the game.
"I have no doubt that he understands the nature of the industry. He's been around long enough to know that and understand that.
"He's been part of many Lions series so it would have been a fitting send off for him, but he'll also have perspective because he's a quality bloke.
"He'll be disappointed and from our perspective it's a little bit of experience gone.
"Those are decisions that aren't made lightly and Warren will have given it due consideration and believes what he has put together will serve him better.
"We have a lot of respect for Brian. He's stung us in the past in 2009, scoring in the last minute for Ireland to draw. He's a class player and class bloke."
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