Mateo Kovacic was left out of Inter Milan's side which was held to a 0-0 draw by AEK Athens on Sunday as he is on the verge of joining Real Madrid.
Kovacic, 21, was expected to start for the Nerazzurri in their final warm-up game before the start of the Serie A season, but he instead spent the 90 minutes on the bench as a precaution.
Real's offer for the Croatia midfielder arrived on Sunday morning, and it has been accepted.
"Unfortunately there are financial fair play rules to respect and I don't think any of us wanted this, but to respect UEFA's parameters we had to do something," Inter coach Roberto Mancini told Mediaset television.
"That does not mean we won't build a side capable of being competitive. We're all sad, from the president down to the players, but given these rules, you have to make sacrifices. I'm sorry if some people can't understand that.
"[Kovacic] and Xherdan Shaqiri have left for the same reason and now we can turn our attentions to something else. Let's hope we can bring in some suitable players quickly because we've got to start playing now, even if the market closes at the end of August. Sacrificing two important players enables us to sign different players in positions where we are lacking."
Kovacic is due to undergo a medical in Madrid on Monday before the transfer can go through, for a reported €35 million plus bonuses.
With Shaqiri joining Stoke City last week for £12 million, Mancini now has the funds he needs to make an acceptable bid for Wolfsburg's Ivan Perisic.
The Croatian has long since been his No. 1 transfer target, only he first had to sell before being permitted to offer the kind of money the Bundesliga club expect.
Perisic was on target for Wolfsburg in their 2-1 win over Eintracht Frankfurt on Sunday.