In a brief statement to reporters Wednesday, Underwood declined to discuss the allegations made by two women after a weekend incident in Lake Delton, Wis.
But he did try to take a step toward making things right with his teammates, six of whom were named in connection with the incident despite being cleared of any wrongdoing.
"I just want to apologize to my teammates who have been dragged into this and I'm sorry that it was a distraction for the team," Underwood said.
Officers were called early Saturday to a condo where players were staying during a charity golf event.
Police cleared six of seven Packers players of wrongdoing and have not named the seventh player or the women making the allegations. Underwood's attorney, Richard Kaiser, told The Associated Press and other media outlets that Underwood is the target of the investigation.
The case took a new twist Wednesday evening, when Lake Delton police said in a news release that "money was exchanged between the alleged suspect and the alleged victims before the alleged assault."
The news release also said that "not all persons interviewed that were at the golf cabin that morning had been consuming alcohol, as had been previously reported."
Kaiser said earlier Wednesday he believes Underwood will avoid being charged with a crime, and police have said they do not plan to recommend that prosecutors press charges because of inconsistencies in the women's statements.
Lake Delton Police Chief Tom Dorner said Monday that the women initially told investigators they were sexually assaulted by more than one Packer while other players held them down. After the players were questioned, Dorner said the women changed their statements to say only one person assaulted them.
The Sauk County District Attorney's Office said Wednesday morning police had not yet turned over the details of their investigation. Dorner did not immediately return a message left at his office.
Players who were in the condo with Underwood didn't appreciate having their names associated with the incident.
"It's very tough, and he's definitely going to have to earn our trust back," linebacker Clay Matthews III said. "But, for the most part, there's not a rift in this team."
Matthews said he appreciated Underwood's willingness to address the team during a meeting.
"Obviously it was his first time addressing the team, not only the team but the individuals that had their name brought up in this case," Matthews said. "I thought it was very sincere, he promised not to be a distraction, he had a sincere apology for not only us but our families and everybody who was in some way affected and which we weren't involved in this. So I thought it was a step in the right direction and, like I've been saying, we're looking to move forward and keep him a part of the team."
Packers coach Mike McCarthy also spoke to the team about the incident.
"We discussed the fact that we are in an offseason program and we're in the paper way too much with things other than football," McCarthy said. "We all have a responsibility and an obligation to represent the Green Bay Packers properly. Every decision we make, both on and off the field, has consequences, and poor judgment was made. With that, the circumstances are what they are. We have dealt with it as a football team and frankly we have moved on."
McCarthy emphasized character when he took over as the team's coach in 2006, often saying that he wanted "Packer people" in the organization. And for the most part, Green Bay players have avoided off-field problems on McCarthy's watch -- until now.
In addition to the Underwood incident, defensive lineman Johnny Jolly is facing drug charges in Houston and tight end Spencer Havner was injured and arrested for suspicion of drunken driving in March after he lost control of his motorcycle.
McCarthy doesn't consider it a downward trend.
"I think they are isolated [incidents], and that's the way you deal with them," McCarthy said. "You deal with everything one day at a time and you make sure that you stay on top of all of the individuals in your program. I think we do a very good job of that here."
Underwood, a sixth-round pick who played sparingly as a rookie last season, recently had earned praise from McCarthy for the improvement he made in the offseason.
"The young man is an ascending player," McCarthy said. "But this isn't all about playing football. There is a lot more to it. The rules of our society dictate that, the rules of the National Football League dictate that, and more importantly, the rules here in Green Bay dictate that, and it's a lesson that he will learn from."