All Blacks captain Umaga and team hooker Keven Mealamu dumped O'Driscoll in an apparent double "spear tackle" after barely a minute-and-a-half of last weekend's first Test in Christchurch.
O'Sullivan, an assistant to Lions head coach Sir Clive Woodward on tour, today revealed that Umaga had spoken to the injured O'Driscoll by telephone but failed to offer an apology for dislocating the Irish centre's right shoulder.
The Lions are already smarting from match commissioner Willem Venter's failure to cite either Umaga or Mealamu over the incident.
O'Sullivan said: "Brian had a call from Umaga and he just kind of commiserated with him being injured as if he had nothing to do with it which I find strange.
"Brian O'Driscoll's tour is over and it ended in a very bad way," insisted the Cork man.
"We can park it there if you want. Things do happen in battle and I accept that. The incident was not premeditated but I think it was opportunistic and I think he knew exactly what he was doing."
O'Sullivan went on to criticise Umaga for not offering an apology to crocked captain O'Driscoll, saying: "He hasn't apologised which is upsetting. There are two things here which Brian is upset about.
"To ring up and say he is sorry that he got hurt without offering an apology is disappointing too. It's like kicking a ladder from under somebody then commiserating he had an accident on a ladder. He was part of it.
"I think Brian is still upset about that and rightly so. You can't change what happened in the cold light of day but he could have handled that better as New Zealand captain."
O'Sullivan added: "We've all had our take on it and this Lions tour will be remembered for this incident so whatever happens from here on in will blight the whole Lions tour and that is unfortunate.
"And even after the event I think it could have been handled a little bit better in retrospect. It's been disappointing."
Umaga yesterday admitted: "While I play hard in all my games, I try and play as fair as I can. That's just the way I am.
"It was an unfortunate incident and these things happen."