The pair have been spotted together several times — including in Los Angeles on March 11 — since calling off their year-long engagement in February.
They were also seen visiting the Demetria Estate Winery in Los Olivos, Calif., over the weekend, where they reportedly weren't trying to hide the fact that they've been hanging out.
"While Shailene has strong feelings for him, she's making it clear it's not a done deal," dishes the insider. The problem, the source explains, is that Aaron, 38, "needs a serious attitude overhaul."
"He can come off as cocky and over-confident, and Shailene has let him know she won't put up with it," the insider adds.
The actress, 30, has been spending time with the NFL star and hearing him out "so he can prove to her that he's not the jerk everyone says he is," the insider adds. "Aaron is a convincing guy, and he promised Shailene he'll change, but he's going to have to make good on his word if he wants to win her back."
Rodgers and Woodley initially called it quits on their engagement after the Big Little Lies star was getting tired of dealing with the athlete's demanding NFL schedule.
"While Shailene is supportive of Aaron's career, he put football first and they were barely spending any time together," a source previously dished. "She felt he neglected their relationship. Neither of them were happy."
However, "now that Aaron is in [the] off season, he has more downtime and can focus more on a relationship," another insider spilled, as OK! learned. "Shailene is understanding and open — she hasn't shut the door completely."
"No one, including them, knows what the future holds — they can possibly get back together or they can decide they aren't meant to be," the source continued. "That's up to them to figure out."
The Green Bay Packers player seemed to be having some regrets over their split shortly after going their separate ways, as he thanked her for her support in an Instagram post days later, writing: "I love you and am grateful for you."
He also issued an apology to Woodley following his COVID-19 controversy, saying he was sorry for getting her and his other loved ones wrapped up in the drama.