Portsmouth have revealed that Middlesbrough paid more than £500,000 to free Gary O'Neil to play for the club again.
O'Neil had played 99 games for Boro, and one more match would have triggered a £1million payment to Portsmouth.
Boro and Pompey held lengthy talks about a compromise, but it appeared O'Neil may have played his last game for the club.
But the two clubs brokered a deal at the weekend, which allowed O'Neil to play against West Brom and Pompey have now confirmed that Boro have paid more than £500,000 as part of the deal.
"We came to an agreement eventually, although we have to keep the details confidential," Pompey administrator Andrew Andronikou confirmed.
"However, they have paid us more than £500,000 and both sides are happy with that."
Despite the outlay of £500,000 on O'Neil, and their failure to get promotion, Boro are still planning to spend some cash this summer.
"We have had two years of rough times here and we have got to say enough is enough now," said boss Gordon Strachan.
"We get on with it, we develop a squad that is consistent. Hopefully, over the next year, we will have a consistent dressing room where there's not much chopping and changing.
"But we obviously have to do stuff in the summer to get a group of players who we know will be here until next summer and that will be beneficial to everybody.
"I already knew what was needed. As a player, captain, manager, coach, I know what's needed to make a dressing room, I know what's needed in the dressing room to be successful and that's what I have got to do, make that dressing room a dressing room that can be successful."