Fletcher Smith said in a statement Thursday that the Shanahans have made comments that go beyond disrespectful and were "unprecedented for a six-time Pro Bowl quarterback such as Donovan."
Smith said in the statement that the Shanahans -- "both Mike and more specifically Kyle" -- have made the quarterback's relationship with them "difficult" to maintain.
"Unfortunately, it appears as though the Redskins coaching staff decided that their 12-year veteran quarterback, who flawlessly executed one of the NFL's most complex offensive systems (in Philadelphia), is unable to grasp Kyle's offense," Smith said.
"I believe there is tension between Donovan and Kyle that's rooted in the fact that Donovan has suggested modifications to Kyle's offense based on intricacies Donovan has learned in his NFL career," Smith wrote. "For example, Donovan has asked all year that the team run more screen passes to help manage the pass rush more effectively. Ironically, Kyle decided to employ Donovan's suggestions after he unceremoniously benched him on Sunday."
Shanahan released a statement in response later Thursday.
"As I stated earlier, when I traded for Donovan McNabb I had hoped that he would lead us to the playoffs," the statement begins. "No one wanted him to be more successful than me. When the team was 5-8 and mathematically out of the playoffs, I made the decision to evaluate our other two quarterbacks. This was not personal, but strictly professional. The decision was made in the best interest of the Washington Redskins and I stand by my decision.
"I will attempt to talk to Fletcher Smith directly to clear up every one of his misconceptions."
McNabb, 34, was listed as the No. 2 quarterback during Washington's 33-30 loss to Dallas. McNabb said he felt "disrespected" by the way he was benched and demoted.
"Everything was handled awkwardly," he said Tuesday on his weekly radio show on ESPN980, "somewhat to a disrespect to me and to the team."
Shanahan waited until last Thursday to tell McNabb that Rex Grossman would be the Redskins' starter for the remainder of the season, although rumblings of a possible switch had circulated all week. McNabb said he believed the team leaked the news before informing him, but Shanahan said Wednesday that he told nobody before he spoke with the quarterbacks.
Shanahan also disagreed with McNabb's assertion that the coach didn't tell him he would be the Redskins' No. 3 quarterback for the final two games.
"I did talk to Donovan (about) exactly what his role was gonna be, just like I shared with (reporters)," Shanahan said Wednesday, according to The Washington Post. "That he was gonna be No. 2 (against Dallas), and then the next two games he was gonna be No. 3 -- and I explained why."
Shanahan continued: "With John Beck getting the reps, just like I did to you guys (reporters), I went into detail about that. I really felt that after I was done, it was a good conversation and we'd go from there."
McNabb was benched only once in 11 years with the Philadelphia Eagles, but he already has doubled that total with the Redskins in less than one season. Shanahan yanked McNabb for Grossman in the final two minutes of an Oct. 31 game against the Detroit Lions, then offered several strange excuses for the decision.
Smith said Thursday the benching of his client has been part of what he described as a "difficult season" for McNabb.
"Donovan is coming off a Pro Bowl season in 2009 where he threw for 3,500 (plus) yards on 60 (percent) completions, with a TD:INT ratio of more than 2:1," Smith wrote. "He also led his team to the playoffs with an 11-5 record, and that's what he hoped to accomplish in Washington.
"This year, Donovan was on pace to set the Redskins all-time passing yards mark before being benched."
Earlier this season, Mike Shanahan said he believed Grossman had a better grasp of the team's two-minute offense, then said McNabb lacked the "cardiovascular endurance" to run a fast-paced drill because of nagging hamstring injuries. Kyle Shanahan, the son of the head coach, said McNabb had been tipped off in advance that the team might go with Grossman; McNabb said he hadn't.
Then the Redskins gave a McNabb a five-year contract extension worth up to $78 million -- although the quarterback is guaranteed only to receive an extra $3.5 million this season. The deal contains a clause that allows the Redskins to cut McNabb before next season with no further financial obligation.
McNabb has expressed a desire to return to Washington next season, and Shanahan said he would be willing to have McNabb as a backup -- a pairing that seems hard to imagine.
But Smith left the door open in his statement, saying McNabb has taken the high road during the circus-like atmosphere.
"Donovan has maintained a high level of professionalism on and off the field," Smith said. "He is determined to continue his relentless commitment to win and looks forward to the opportunity wherever that may be!"
The Associated Press contributed to this report.