Not sure I entirely agree with that.
-Mike has the burden to demonstrate that something defamatory was said about him by Marriot to the NFL. This burden is fairly heavy--he needs to prove his case in his case-in-chief or it gets tossed before the defense gets to put on their case. HASN'T THIS ALREADY BEEN DONE? MARRIOTT SAID THAT HE SAID XYZ TO HER. AND MARRIOTT REPEATED THAT TO THE NFL (PRESUMABLY).
-Once he meets that burden, then it is the burden of Marriot to demonstrate that something was conveyed to them by the lady that caused concern. This is likely a relatively easy burden met with simple testimony by a Marriot employee that "xyz" was conveyed to them. Then, it turns into a credibility battle between the young lady and Michael re: what was said. (Hence why I think this is a risky proposition.) Anyways, if a jury determines she is credible, Michael's case is likely over. THIS IS WHERE I THINK MARRIOTT CANNOT MEET ITS BURDEN
I've simplified it and cases can take turns (if, for example, Marriot misrepresented what she said to the NFL or Marriot ran with it without conducting its own investigation) but I'm keeping it big picture.