Former Canterbury-Bankstown winger Matt Utai, who starred in the team's 2004 premiership, was ambushed at his home at Greenacre, in southwest Sydney, with no motive immediately clear.
He underwent surgery after being left with serious leg wounds from the attack, which happened about 6am on Tuesday.
Local police handed the investigation into the "brazen ambush" over to the organised crime-focused Raptor Squad, Superintendent Rodney Hart told reporters.
But a motive remained unclear, with Utai having no clear links to criminal activity.
"This was definitely targeted," Supt Hart said.
"Whether the victim was the intended target or it was somebody that he knows or associates with or is related to will all form part of the investigation."
Police were told shots were fired from an SUV that was later found burnt out.
Utai starred in the 2004 NRL grand final, scoring two tries as his Bulldogs knocked off the Sydney Roosters.
His former club said it was deeply shocked and saddened to learn of the shooting.
"Matt is a beloved part of the Bulldogs family ... he played 127 first-grade games for the club and was instrumental in the 2004 premiership," the club said in a statement.
"Our thoughts are with Matt and his family during this extremely difficult time.
"We are hoping and praying for his full recovery."
The New Zealand and Samoa international played 167 NRL games, joining the Wests Tigers in 2011 and spending three seasons there.
Two Tigers teammates - Beau Ryan and Aaron Woods - were live on radio when they learned of the shooting and were audibly shocked.
"It's still very raw ... I can only imagine what Matt's family (are feeling), he's got kids, he's got a lot of family there," Ryan told Triple M Sydney.
"He's got a lot of ex-teammates ... we are praying and hopefully he makes a recovery, it's tough times."
Woods said Utai remained a great mate.
"I still talk to him a lot in this day and age, so it's actually rocked me a little bit," he said.
Utai walked out of the home he shares with his wife and children and was about to drive to work when he was shot.
He was in a fair bit of pain but able to speak with arriving police who applied first aid, Supt Hart said.
Utai was stabilised by paramedics and taken to hospital in a serious but stable condition before undergoing surgery.
The SUV involved in the attack was found after being set on fire less than a 10-minute drive from where the shooting took place.
Fire authorities extinguished the blaze and the SUV was seized for forensic examination.
The 2002 Dally M Rookie of the Year finished his NRL career with 85 tries.
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