O'Neil, who has chalked up 99 appearances, trained with the rest of the Boro squad yesterday after manager Gordon Strachan had given his players a couple of days off following a fruitful four points over the Easter period.
But the Middlesbrough captain is having to carry on his day-to-day duties at Rockliffe Park, despite knowing last weekend's outing against Crystal Palace could be his last for the club.
Strachan remains full of admiration for the former Portsmouth man and would prefer to have his skipper involved in all four matches in the final month of the campaign.
But he is unlikely to be given the go-ahead to include O'Neil against Sheffield Wednesday at the Riverside Stadium tomorrow, unless there has been a major breakthrough with Pompey.
Strachan is being regularly updated by chief executive Keith Lamb about the situation.
Portsmouth knocked back Middlesbrough's initial proposal last week, which it was claimed amounted to £20,000 for each of the remaining four matches.
I don't need to say anything else, the situation speaks for itself. I have spoken about it. That's it, said Strachan yesterday.
I would think Gary wants to play, he is a top, top pro. I know what the situation in the table is all about, I know how important it is. I'm a big boy, I'm 53 now.
As I said earlier, I'm in charge of the football team, they are in charge of the financial side, we will get together and decide what is best for the club. We speak together every day. We are doing OK.
Boro sit six points off the play-offs with 12 points to play for.
But with sixth-placed Leicester City due to travel to Peterborough who installed new boss Gary Johnson this week and Blackpool heading to leaders Newcastle, this could be the make-or-break weekend for the Teessiders.
Strachan would prefer to play O'Neil in all of four matches but, with Premier League football next season unlikely, it would not make financial sense to play him now, triggering the final £1m payment on the £4m deal agreed in the summer of 2007.
Boro still hope to convince Portsmouth to back down but O'Neil who would face an automatic two-match ban if he picked up a yellow card in tomorrow's match only looks destined to figure again this season if a play-off place is secured.
Strachan expects £3.5m striker Scott McDonald to return to the starting line-up against Wednesday, after emerging as a substitute in the win at Plymouth on Monday to protect his sensitive hamstring.
It was a victory made more impressive by the fact that a number of players were carrying knocks and the fact that in the build up Strachan was told not to field O'Neil.
We had a lot of problems going into Monday and the big players dragged us through it, said Strachan, also expecting Andrew Taylor to be available again after a groin niggle.
The surface was not conducive to good football, but we somehow turned out some decent passing stats.
It was satisfying because there was a lot to be dealt with over the weekend, injuries and suspensions and circumstances you don't normally have to deal with. It was a good performance.
We are becoming harder to beat, but we need to learn how to win games better and that's in the final 25 yards of the pitch.
If we can deal with that and cut out a lot of individual mistakes we have made through inexperience, really we will be growing.