Unless Boro chief executive Keith Lamb comes back with a much improved offer there is no possibility that ONeil will feature in tomorrows crucial encounter at the Hawthorns and in all probability the captain has played his last game for the club.
A clause in the deal that took ONeil from Fratton Park to the Riverside in 2007 stipulated a 1m payment was owed to Pompey once the 26-year-old played 100 games for Boro.
Since making 99 appearances for the Teessiders, ONeil has been sidelined with Boro understandably reluctant to commit themselves to paying the 1m fee.
Administrator Andrew Andronikou insisted he remains on amicable terms with Lamb but admitted he had been disappointed by Boros offer and claimed that the onus was now on the club to come back with what he termed "a realistic proposal."
Gordon Strachan had earlier sounded an optimistic note a deal could be reached that would allow him to field his influential skipper for the rest of the campaign, but Andronikou does not expect an eleventh hour deal to be agreed.
"Dont get me wrong, I want Middlesbrough to have access to Gary but it seems to me that they are posturing because we are in administration and think that any offer they make is better than nothing," noted Andronikou.
"That is not how I regard the situation. Their mentality seems to be that they are in a strong position but I must do what is right for the club. I do not expect Gary will play at West Brom this weekend."
Strachan stressed this week that the club would employ a prudent approach to financial matters.
"We need to be organised so the club is never at risk, I'm not saying it is. We don't want to be at risk like other clubs are. I'm not an economist but we will live within our means," said the manager.
The administrator claims that he took the initiative to contact Lamb to thrash out a deal that would allow ONeil to pay and give Pompey recompense.
But protracted discussions on Wednesday failed to bring the parties any closer to agreement and it seems that Boro must face their battle to reach the play-offs without one of their most important players.
Andronikou would not reveal the precise terms of the offer on the table from Middlesbrough but confirmed that it was so far below his valuation that he was now concentrating his efforts on handling other matters relating to the cash-strapped south coast club.
He continued: "I took the initiative with Mr Lamb. I contacted him and put what I believe is a reasonable offer but Middlesbrough's proposal fell well short of that.
"I was disappointed with their offer. The structure of the deal they put forward was unacceptable to us. I spoke to Mr Lamb a couple of times on Wednesday.
"It would be a different scenario if Gary had only played a few matches but he has played 99 games for them and has been an important part of their side. They can sell him this summer. In my opinion, Middlesbrough are unrealistic.
"With all due respect to Middlesbrough I have so many other matters to deal with regarding Portsmouth I don't have time to become involved in protracted negotiations with them. The ball is now in their court and unless they come back with a significantly improved offer then that is an end to the matter.
"We are still on amicable terms but I dont see why we should accept an offer that we dont believe is in the best interests of Portsmouth Football Club.
"Unfortunately their offer was miles away from what we expected."