While the Boston Celtics got Gordon Hayward back in the lineup Monday against the Cleveland Cavaliers, they lost Marcus Smart after the guard suffered an apparent eye infection prior to the game.

Smart has been the defensive anchor for the Celtics this year and has endeared himself to fans with his tough play, perimeter defense and hustle on both sides of the ball.

At 17-5, Boston has exceeded the expectations of many as the current No. 2 seed in the Eastern Conference. A big part of the Celtics' early success is their stifling defense. Boston currently ranks second in the NBA in points allowed per game with 102.8 and third in defensive rating.

If the Celtics want to continue their reputation as one of the best defensive teams in the NBA, the health of Smart is imperative. Something that is up in the air for the team's next game on Wednesday against the Indiana Pacers.

Despite being questionable to play against the Pacers, Celtics head coach Brad Stevens is confident that the 6-foot-3 guard will be back sooner than later.

“My assumption was that it should be something that will be able to be taken care of quickly…we're hopeful he will be able to play,” Brad Stevens said, per Brian Robb of the Boston Sports Journal.

In his sixth NBA season, the fiery 25-year-old is averaging 11.8 points, 4.8 assists, 3.4 rebounds and 1.3 steals. Despite shooting just 38.7 percent from the field, Smart has been one of the Celtics' most important players this season as much of his impact doesn't show up on a traditional stat sheet.