Baseball's active home run leader had surgery to remove a bone spur in October and Griffin said the team's designated hitter is "better now than he was at any time last year.
"He knows how to lose some weight, and when I last saw him, he had lost six or seven pounds."
Griffin made his comments about Griffey during Thursday's pre-Spring Training media session at Safeco Field.
Griffey, who returned to Seattle last season after being away for 10 seasons, batted .214 with 19 homers and 57 RBIs in 117 games. He was a designated hitter for all but the first weeks of the season, appearing in just 11 games in the field.
"A lot of people don't understand because they weren't in the clubhouse how bad his knee was last year," manager Don Wakamatsu said. "There were times when it was swollen and he couldn't play. The good news was right after the season when he had the surgery and he feels like he's in tremendous shape."
Wakamatsu said Griffey "feels that the surgery was great success, so in that we are looking for some production out of him."
Griffey, who has 630 career home runs -- fifth on the all-time list -- had his knee drained of fluid several times during the 2009 season.
Mariners pitchers, catchers and players, including Griffey, coming off injury or surgery last season can report to Spring Training on Feb. 17 in Peoria, Ariz.
It is not known if Griffey would report then, or on Feb. 23 when the remainder of the team reports to camp.
In other medical news from the team, according to Griffin:
Reliever Sean White: "He currently is throwing four days a week from about 120 feet and we anticipate him going to camp and competing for a position. He will progress slowly out of the gate."
Starter Ryan Feierabend: "He had Tommy John surgery and is about 11 months post-surgery. It normally takes 10 to 12 months of recovering time, so he is right in that range and has been throwing bullpens. Once we get down to Arizona, we will evaluate him closely. But we anticipate him being able to compete for a position. He has been working real hard in Arizona.
Reliever Chad Cordero: "He continued to work this offseason on his arm strength and also got himself in a lot better condition, losing about 20 pounds. He will come to camp with no restrictions and compete for a position."
Catcher Luis Oliveras: "He came into camp last year with a torn ACL and needed surgery. He lost almost all of Spring Training and a majority of the regular season. He went to winter ball and caught, so he will be coming into camp 100 percent and ready to go."
Erik Bedard: "I actually talked to Erik this morning. He is playing catch and said he feels very good. He has been working with the same therapist in Canada and says he feels very good. He's not on a throwing program, but is doing all of his conditioning. When he had his surgery last year, Dr. [Lewis] Yocum said it was a 10- to 12-month rehab program and he's at about seven months now. He has a ways to go.
Outfielder Endy Chavez: "Endy actually is going to be here next week. He's a free agent, but we're responsible for his rehab and care. He's working hard. He has started running, straight ahead, doing agility drills and will see Dr. [Ed] Kahlfayan on Monday. Afterwards, he probably will start to do some functional things, like batting practice. He'll go to New York and continue his rehab."