O'Neill is yet to sit down with owner and chairman Ellis Short to discuss his summer rebuilding plans, and expects to do so as the current season draws to a close.
However, while he knows in which areas he would like to strengthen, he wants to retain the key men who have driven the recovery he has prompted since his arrival at the Stadium of Light in December.
O'Neill told the Sunderland Echo: "I really don't want to go down the road of telling people that this is set in stone or that is set in stone and then find myself being put on the spot a few months later when this happens or that happens.
"The modern game moves so quickly that just about anything can happen.
"But I'm happy to say the owner agrees with me that we want to keep our very best players at the club because we are looking to build something here and move forward.
"You don't tend to do that if you are selling your best players.
"We have a squad in a process of development. We have a lot of work to do, and I think it is clear that we need to strengthen.
"We remain very much a club that is looking to go forward."
The retention of star man Stephane Sessegnon in particular will be a priority for the Black Cats after recent speculation linking him with former club Paris St Germain and Arsenal.
Sessegnon has been touted as a potential target amid rumours that he has not settled in the north-east, although O'Neill insisted only last week that the Benin international could not be happier.