Moss found his starting spot at the Redskins under threat last season following the arrivals of Pierre Garcon and Josh Morgan, prompting him to lose weight and get in the best possible shape ahead of the 2012 campaign.
Shanahan has revealed that the 34-year-old has continued that regime during the current off-season and believes that he will be able to play at a "very high level" this year.
"Last year and this year he lost a good 10 pounds. He decided to be in the best shape he could possibly be in," he told reporters.
"He had a great off season and you see the dividends from being in great shape. He has continued to do that this year. He is in excellent shape.
"You can see some of the plays he has made thus far at camp, see that he is hungry and he is going to play at a very high level."
Moss has been at the Redskins for eight seasons and has scored 45 touchdowns.