In this Nov. 28, 2013, file photo, Detroit Lions wide receiver Calvin Johnson (81) is defended by Green Bay Packers cornerback Sam Shields during an NFL football game in Detroit. Signing a four-year, $39 million deal with a $12.5 million signing bonus can be a life-changing event, especially for the fifth-year undrafted cornerback Shields who didn't move to defense until his last year in college.

GREEN BAY — Cornerback Sam Shields' position coach nearly cried when he let him know he had re-signed with the Packers. Shields' mother bawled when she learned of the deal, and he bought her a house.

Signing a four-year, $39 million deal with a $12.5 million signing bonus can be a life-changing event, especially for a fifth-year undrafted cornerback who didn't move to defense until his last year in college.

Now it's time for Shields to assume the pressure that comes with a big deal.

"The reality of it is Sam is now looked on as one of our core players," coach Mike McCarthy said Tuesday. "So he'll step up and play accordingly."

Shields didn't cry after agreeing to the contract in March.

"I promise I didn't," he said after a team workout. "It's still ... it's like 'Dang, wow.' But I didn't."

Shields seems to be handling the attention well. He said he feels no extra pressure with the contract, and that he's confident that his best years are ahead of him.

Just the kind of attitude that McCarthy would like to hear as Green Bay tries to improve its defense. The return of Shields gives the Packers stability at corner, with veteran Tramon Williams manning the other side.

Shields, who has 13 interceptions in four years with the Packers including four last year, said he is still learning. Imagine if Shields had played corner his whole career. After making 75 catches for 971 yards and seven touchdowns in his first three seasons of college ball at Miami, Shields was asked to move to corner after the spring game before his senior year. Shields played defensive back in that game, and an assistant coach liked what he saw.

His family encouraged him to try it, and Shields went on to start 10 games at corner. In April 2010, the Packers signed him as an undrafted free agent.

There were some discouraging moments in the beginning. He would argue with cornerbacks coach Joe Whitt about learning the plays.

"When I first got here, I didn't know the difference. It was frustrating. 'Man, it's not for me,'" Shields recounted.

But Whitt stuck to it, even making little cards to help Shields study the defense. Shields gives Whitt the most credit for his development and his prized pupil is now returning to Lambeau Field with a new deal.

"Sam Shields has earned this opportunity. I think he'll handle himself and clearly understands the level of success ... the step that he's taken," McCarthy said. "But frankly, we all know there's so much more out there that we want to accomplish."

Losing Shields could have meant that Casey Hayward, who missed most of last season with a hamstring injury, would be moved into the starting job; or Micah Hyde, who had a promising 2013 season after being drafted in the fourth round a year ago.

Instead, Hyde is now getting looks at safety, along with 2014 first-round pick Ha Ha Clinton-Dix. Shields' good friend, veteran Morgan Burnett, signed a big free agent contract last year, and returns at the other safety spot. The Packers are looking for more big plays from their safeties, a position from which the team didn't get an interception in 2013.

Notes: Rookie TE Richard Rodgers impressed at the open workouts with reaching out with an outstretched left arm to catch a pass while on the run on a crossing pattern. "I think he's going to push for some playing time If he can transfer what he's done in the spring now to the fall and have the potential to be an impact player," quarterback Aaron Rodgers said. ... Backup TE Ryan Taylor made a nice juggling catch up the seam on a pass from backup QB Scott Tolzien that went through a defender's hands.