The 30-year-old wing-back, who played 22 minutes in Croatia's Euro 2012 group stage exit, said making way for uncapped Dinamo Zagreb playmaker Sammir was the "final straw" after Stimac also left him out of Croatia's opening two World Cup qualifiers.
"It was a tough decision to make but being ignored to fit in Sammir at my expense is more than I can take because I was also cold-shouldered for the opening two games with Macedonia and Belgium," Pranjic told Croatian media on Friday.
"I felt strange because Stimac told me ahead of those two games I was going to play a part in both and after I was left out, I said to myself I would walk out if Sammir was called up.
"I have nothing personal against the lad, I know he is a good player but I can't accept this way of doing things."
Sporting's Pranjic has failed to score in 45 international appearances and was last a regular starter on the left flank during Croatia's futile World Cup 2010 qualifying campaign.
Sammir, 25, joined Dinamo in 2007 after nondescript spells with several Brazilian clubs as a youngster and became one of the team's key players in helping them win a record seven successive Croatian league titles.
He was selected for a Brazil youth team so Stimac said Croatia were talking with FIFA to make sure his papers are in order and he is eligible.
Stimac, who took over from Slaven Bilic after Euro 2012, said he included the flamboyant playmaker - known for his late night clubbing as much as for brilliant free kicks and close control - to give him a chance to prove his worth.
"This is a opportunity for him to change his lifestyle and make an impact because we know he can be a better player than he is at the moment," said the 45-year old coach.
"We also know he's had problems with his lifestyle but whether he turns a new leaf and lives up to expectations is now entirely up to him and he will have to work hard because the competition within the national team is fierce to say the least."
Croatia, who are joint top of Group A alongside Serbia and Belgium with four points from two games, visit Macedonia in Skopje on October 12 and host Wales in Zagreb four days later.
Even if he is cleared by FIFA in time for the double-header, Sammir is likely to start on the bench with Real Madrid playmaker Luka Modric rediscovering his form after a protracted move to the Spanish champions from Tottenham Hotspur.
26-man squad:
Goalkeepers: Stipe Pletikosa (Rostov), Danijel Subasic (Monaco), Dario Kresic (Lokomotiv Moscow).
Defenders: Vedran Corluka (Lokomotiv Moscow), Darijo Srna (Shakhtar Donetsk), Josip Simunic (Dinamo Zagreb), Gordon Schildenfeld (Dynamo Moscow), Ivan Strinic (Dnipro Dnipropetrovsk), Domagoj Vida (Dinamo Zagreb), Dejan Lovren (Olympique Lyon), Manuel Pamic (Sparta Prague).
Midfielders: Ivan Rakitic (Sevilla), Milan Badelj (Hamburg SV), Niko Kranjcar (Dynamo Kiev), Ognjen Vukojevic (Dynamo Kiev), Luka Modric (Real Madrid), Ivo Ilicevic (Hamburg SV), Ivan Perisic (Borussia Dortmund), Josip Radosevic (Hajduk Split), Sammir (Dinamo Zag
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