Modric has been the subject of intense transfer speculation this summer, but as of yet no club have reached the £40 million asking price Spurs are demanding for his signature.
Modric refused to travel to the United States for Spurs' tour and has not been picked for any of the club's other pre-season games since.
That has not gone down well with national head coach Stimac, who plans to give the 26-year-old his first game of the summer on Wednesday when Croatia face Switzerland in Split.
"I don't like the situation that he is in at all, he has not played any matches at all this summer," Stimac was quoted as saying on AS.com.
The former West Ham defender said he is confident the player will leave White Hart before the end of the month, however, adding: "He will end up signing for Madrid before the market shuts."
Tottenham already appear to be planning for life without Modric. The Londoners signed Gylfi Sigurdsson from Hoffenheim earlier this summer, and it is understood they have launched a bid to sign hard-working Rennes midfielder Yann M'Vila.
Although the capture of M'Vila would undoubtedly improve the strength of the Spurs squad, Villas-Boas' main concern is in the striker department.
Jermain Defoe and rookie Harry Kane are the only strikers on Tottenham's books as efforts to sign Emmanuel Adebayor and Leandro Damiao have so far failed.
Spurs have also made an offer for Gaston Ramirez, according to the Bologna forward's agent.
"The only solid offer is the one from Tottenham, who offered 16 million euros [£12.6m]," Betancourt told Calciomercato. "But the deal didn't go through because Spurs offered too low a wage to the player and if the wage difference is minimal he would stay at Bologna.
"Tottenham could raise their offer if they sell Modric and in that case the deal could be done, otherwise Ramirez will stay another year at Bologna. We also talked with Liverpool but nothing more.
"Inter Milan are interested in the player, but can not afford to offer cash as the teams in the Premier League."