Already boasting a 2-0 series lead over the Brooklyn Nets, the Celtics may get a key defensive reinforcement back as soon as Game 3 on Saturday.Robert Williams has not played since suffering a lateral meniscus tear in his left knee on March 27, which required surgery on March 30.The Celtics gave him an initial return timeline 4-to-6 weeks. A Game 3 return would be well ahead of schedule, at just over three weeks.Lateral meniscus tears take longer to recover from than medial meniscus tears, thus the ProBasketballDocs projected in late March that the Celtics' center would be 100% around the six-week end of that timeline.It is certainly encouraging news that Boston plans to bring him back in limited minutes as soon as Saturday. Williams has reportedly played 5-on-5 in consecutive practices without any lingering pain.Still, the 24-year-old is less than 100% at this point in his recovery and will continue to have limited mobility, possibly until the start of the Eastern Conference Finals.If he suits up for Game 3, Williams will carry a Sports Injury Central health score of 57. That number is likely to build over time and Williams gets up to speed and as his left knee continues to heal.Williams was second in the NBA in blocks per game during the regular season and third in offensive rebounds per game. Daniel Theis and Al Horford have done an admirable job of anchoring the defense with Williams out, but his production when healthy cannot be replicated.As of Friday, the Celtics are 3-point underdogs for Game 3 in Brooklyn and the over/under is 222.5, according to FanDuel Sportsbook. The Celtics are favored at -550 to win the series.