Both Bündchen, 42, and Brady, 45, have enlisted divorce lawyers, PEOPLE has confirmed, and the supermodel has been working with hers for "awhile," the source says.
"Gisele has been talking to a divorce lawyer for awhile but to my knowledge has not filed anything and is still talking to Tom about their issues," the insider says, adding: "This is not something that just happened today."
They add that hiring a lawyer does not necessarily mean the couple will go through with a divorce.
"Many people talk to lawyers but don't go through with it when the realities of money set in," the source continues. "But in this case, both sides have plenty, and it isn't one-sided, so it could be a different situation."
On Tuesday, PEOPLE reported that Bündchen hired a divorce attorney amid their marriage troubles, and Brady, her husband of 13 years, was "trying to figure out what to do."
Page Six was the first to report the news.
Michael Stewart/FilmMagic Tom Brady, Gisele Bundchen
The couple, who share two children — son Benjamin Rein, 12, and 9-year-old daughter Vivian Lake, along with Brady's son John Edward, 15, with ex Bridget Moynahan — have been dealing with "a lot of tension" in the marriage, in part because of Brady's decision to return to the NFL this season after a brief retirement.
"She was so happy when he announced his retirement," a source told PEOPLE in September.
If they do decide to divorce, the couple will have to sort out their multimillion-dollar assets, such as their four homes, divorce attorney Sue Moss with Chemtob Moss Forman & Beyda LLP, who is not connected to the couple, told PEOPLE on Tuesday.
"The big challenge for him is everything will be determined at the height of his income, because to get him to come back, the Tampa Bay Buccaneers had to come up with a lot of cash — and that is the baseline for determining the support in this case," Moss said.
Never miss a story — sign up for PEOPLE's free daily newsletter to stay up to date on the best of what PEOPLE has to offer, from juicy celebrity news to compelling human interest stories.
"At the beginning, Gisele was earning more than him, and he kept on winning and his income got more and more substantial and it outgrew hers," Moss told PEOPLE. "And because of the timing, the case will be determined based upon the height of earnings."
According to NYC divorce attorney Jacqueline Newman of Berkman Bottger Newman & Schein LLP, who is not connected to Brady or Bündchen, a prenuptial agreement is likely already involved, given the powerhouse couple's massive net worth.
Andrew H. Walker/Getty
"People of this magnitude of wealth don't generally get married without a document that's going to dictate what's going to happen if it doesn't run its course," Newman told PEOPLE.
"My guess is that a lot of this is already worked out. So, there's probably a prenuptial agreement that's going to dictate a lot of this, but if there are some properties that were purchased while they were married — marital residences — there may be fights about that," Newman added.
"There probably were assets that were acquired during the marriage, so there may be squabbles about that to say the least," Newman told PEOPLE. "That said, I think they are going to settle this, assuming they go forward with it — outside of the press."