The Milwaukee Bucks were expected to at least come away with one win during their back-to-back set on Sunday and Monday against the Brooklyn Nets and Boston Celtics, respectively. However, they fell short in what ended up being a trap game against the Nets, and the Celtics matchup is as unforgivable as it can be on the second night of a back-to-back. Thus, it wasn't a huge surprise that the Bucks lost against the reigning champion Celtics as well, 119-108.

Now, it's too early for the Bucks, a team with championship aspirations, to hit the panic button even though their 1-3 start to the new year is far from ideal. For head coach Doc Rivers, he simply chalked this one up to running out of gas especially when the Celtics have the rest advantage over them.

“I don't like moral victories, but I just thought that's what we can be – at least for three quarters. I thought we kind of ran out of gas a little bit,” Rivers said, per Eric Nehm of The Athletic.

Rivers did not sugarcoat matters; he felt as though the Bucks' bench was lackluster against the Celtics, which forced him to pump more minutes into the team's best players (Giannis Antetokounmpo and Damian Lillard played 39 and 36 minutes, respectively), causing them to become exhausted more quickly.

“[We] didn't get a lot of help tonight from our bench, so we extended minutes,” Rivers added.

The Bucks, at the very least, could look forward to the return of Khris Middleton to at least restore a better sense of balance into a top-heavy roster. But for now, they will have to endure these growing pains as they look to restore the identity of their team.

Is it time to be concerned for the Bucks?

The tandem of Giannis Antetokounmpo and Damian Lillard should be the among the very best in the league, at least on paper. Their skillsets perfectly complement that of each other's. But it is indeed a major concern that the Bucks have struggled to begin the season even though Antetokounmpo and Lillard have been teammates for over a year.

The Bucks' depth is far from the best, and it's evident that everything has to go through Antetokounmpo or Lillard for good things to happen on the offensive end. Meanwhile, they don't have too many quality defenders to help hide the defensive downgrade from Jrue Holiday to Lillard.

Now, only four games have passed on the season, so it's too early to be panicking. But there are indeed plenty of valid reasons to be concerned over their long-term contending prospects.