Al Horford is the oldest player on the Boston Celtics roster. He is a five-time All-Star and a veteran with 11-plus years in the NBA. Yet, even Horford is having a hard time figuring out why such a young and talented Beantown team has been so disappointing this season.

When asked point-blank about Boston's biggest issue following the team's 115-104 loss to the Houston Rockets, Horford was practically at a loss for words:

The Celtics have now lost five of their last six.

One thing is for certain: Horford's play is certainly not an issue. The 32-year-old continues to play tough interior defense and scores when called upon, posting a career-high .572 Effective Field Goal Percentage. He posted 19 points and six boards in the loss on Sunday.

But Al Horford lacks assistance in the frontcourt. Aron Baynes returned to action on Sunday but played just 12 minutes and will need time to adjust to the action. Daniel Theis has been steady, but not so reliable for long stretches. And Marcus Morris plays more from the perimeter.

More significantly, Jayson Tatum has not scored more than 14 points in his last five games. Despite being more assertive on Sunday, Tatum shot just 5-15 from the field in a disappointing performance.

The Celtics rank 10th in offensive rating and remain in the top five in terms of defensive rating, yet they simply have struggled to string together good performances.

If even Al Horford is puzzled by Boston's troubles, the Celtics can only hope that head coach Brad Stevens can find the remedy…and soon.