Mack, an All-American from California who also can play guard, was on the practice field just hours after signing with other rookies called in early by new coach Eric Mangini.
The 6-foot-4, 311-pound Mack won the Draddy Trophy, which is given to college football's top scholar-athlete, and was a two-time finalist for the Rimington Trophy, given to the nation's top center.
Mack worked out briefly at guard at the Senior Bowl but lined up only at center at Browns minicamps, eventually playing center with the first team. For the upcoming season he could replace starter Hank Fraley, a nine-year veteran who struggled last season in Cleveland's 31st-ranked offense.
As a senior in 2008, Mack didn't allow any sacks or quarterback pressures on 397 pass plays. He was the Pac-10's Scholar-Athlete of the Year in 2008 and was a four-time league academic honor roll honoree.
On Friday, the Browns signed linebacker
Kaluka Maiava, a fourth-round draft pick from Southern Cal.
Maiava, not as well-known as some of the Trojans' other
linebackers, was present for the first day of rookie
A second-team All-Pac 10 selection as a
senior, Maiava had 66 tackles and an interception last season.
The Browns' veterans are not required to report until July 31,
and first-year coach Eric Mangini will have his first practice on
The team also announced it had waived linebacker David Holloway.
The Browns were one of the NFL's biggest disappointment last year. They finished 4-12 after a surprising 10-6 finish the year before.
Information from The Associated Press was used in this report.