In terms of players the Packers can ill afford to be without the rest of the season, undrafted rookie Sam Shields might deserve to be near the top of the list, according to daily team observers. Shields, whose 4.28 40-time could make him the fastest player in the league, has done a solid job as the Packers’ third cornerback since coming back from a calf injury that forced him to miss games against Detroit and Washington. Plus, he is being counted on — at least for the time being — to handle the team’s kickoff-return duties after displaying Devin Hester-like flashes in that role against Dallas with an eye-opening 49-yard kickoff return. Shields has earned a second chance at succeeding in the KR role after having a very hard time holding onto the ball in training camp and the preseason. But after making steady strides in practice, his value to the team in a dual role could be a key down the stretch.