SAN FRANCISCO -- Boston Celtics coach Brad Stevens gave his 12-year-old son, Brady, a Christmas gift last month that any young NBA fan would covet: tickets to a Golden State Warriors game. But don't get the wrong idea about the younger Stevens' rooting allegiance.

"Let's get this straight, he was wearing Kyrie [Irving] shoes today," Stevens said Friday with a smile.

Indeed, Brady was sporting a pair of Nike Kyrie 4 "Confetti" sneakers while he and pal, Braeden Shrewsberry, son of Celtics assistant coach Micah Shrewsberry, got shots up on the campus of the University of San Francisco following Boston's offday workout.

The young duo got a brief respite from school obligations to be inside Oracle Arena on Saturday when the Celtics visit the defending champion Warriors (8:30 p.m. ET, ABC).

You'd think the biggest challenge facing the elder Stevens would be game-planning to slow Golden State's otherworldly offense, the one that captivates NBA fans of all ages while posting a league-best offensive rating of 113.8 this season.

No, Boston's biggest concern is its own offense.

Masked by both a league-best defense and a lofty spot atop the Eastern Conference, the Celtics have been the league's worst offense in the month of January, a brutal nine-game stretch in which Boston has struggled to score with any sort of efficiency.

The Boston Celtics are looking to sweep the Golden State Warriors, but their struggles to score lately are a major hurdle. Harry How/Getty

When Gordon Hayward was lost to a fractured ankle in the opening minutes of the 2017-18 season, it was obvious that Boston's offense wasn't going to be as potent as expected. For a Celtics team that didn't have a secondary creator to pair with Isaiah Thomas in recent seasons, Hayward's addition was supposed to end the maddening lulls that often occurred when Boston had its All-Star point guard on the bench.

Right now, it's the same old story. Even though the Celtics swapped Thomas for Irving in August, Boston is enduring similar troubles whenever Irving goes to the bench. The Celtics, their depth depleted in the Irving deal, have been forced to lean heavy on inexperienced players and, not surprisingly, the results have been inconsistent. Stevens lacks the sort of secondary scoring threat that he might have been able to stagger with Irving.

Boston owns an offensive rating of 108.2 with Irving on the floor this season, according to NBA Advanced Stats. That's tied for the best on-court rating on the team with Al Horford, and is nearly four points higher than Boston's season average.

But when Irving goes to the bench, Boston's offensive rating dives to a team-worst 97.2. That means Boston is 11 points better per 100 possessions with Irving on the floor.

Boston's Irving-less struggles are particularly pronounced this month. For the month of January, Boston's offensive rating is an impossibly low 86.4 when Irving is not on the court. In the one game he missed because of shoulder soreness, Boston was held to a season-low 80 points in a loss to the Philadelphia 76ers.