Heading into Monday, the Boston Celtics rank second in the Eastern Conference with a 42-19 record.With a 21-11 mark in front of their home fans at the TD Garden and a 21-8 clip on the road, the Celtics' degree of success has been a pleasant surprise for their fanbase.Considering the fact that All-Star forward Gordon Hayward was lost due to a gruesome ankle injury in the season opener, what coach Brad Stevens has been able to do with Kyrie Irving, Al Horford and a slew of young players has been simply sensational.But lately, Boston has seemed a bit flat. In fact, they have gone 8-9 in their last 17 games. That's not a good sign. Something seems to be off.Here are three valid concerns that the team must address before their playoff run. If they don’t do so, not only could their chance at an 18th overall championship be erased, but they might not even get out of the first round.

Utilizing Greg Monroe

When the Celtics signed veteran big man Greg Monroe after his contract was bought out by the Phoenix Suns, it was regarded as a huge signing. Instead, he has averaged 5.7 points and 4.7 rebounds over 13.7 minutes in six contests with Boston. During his 52 minutes on the court, the Celtics have also been outscored by 5.9 points per 100 possessions.

Most of all, Boston needs to figure out how he fits into a rotation. The team has had success starting Aron Baynes at center for most of the season and Al Horford has put forth an All-Star campaign. Others like Daniel Theis and Marcus Morris have taken on large roles off the bench recently.

"It's not gonna be a puzzle," Stevens said before a team shootaround Friday morning, per Jay King of MassLive.com. "You go to what you think will give you the best chance of winning on a given night. I guess I look at it as more of a great opportunity from a standpoint of there may be some matchups that are difficult for some guys and (it) may be somebody else's night. The bottom line too is we're one long injury or time missed away in the frontcourt from being really thin. So we knew that going into the trade deadline and all that stuff. Greg's obviously a really good player who can certainly help us.”

"I think the biggest thing is being patient with everything, because it's not going to come overnight," Stevens continued. "One thing is you can study and know the playbook and do that stuff all you want, but it's really about getting into playing with the other guys that are here, and that's really hard. And obviously when you do it out of a break, it makes it even more difficult, because everybody's gone for a week. But he's a really smart guy so as far as picking things up and knowing what we're trying to do, that's going to be really quick with him. Then it just becomes about who complements who the best and everything else."

It’s worth noting that Stevens started Monroe alongside Horford in the team’s recent overtime against the Washington Wizards. Therefore, some more experimentation will likely occur in the coming weeks as Stevens decides how to best utilize Monroe’s undeniable skill set on the low block.

Overall rotational changes

Before the All-Star break, Stevens made it clear that he and his staff will explore and potentially change entire rotations if it becomes necessary.

"It's going to be a tough ending if we don't change a little bit, and I'll look at what I can change, as well," Stevens said after a loss to the Los Angeles Clippers on February 15, per Chris Forsberg of ESPN. "I think we're probably due for some of that.”

"We'll look at everything," Stevens added. "Obviously, you're always looking for small tweaks defensively and offensively, but we haven't gotten enough out of our rotations and subs and all those things. We'll take a deeper dive into that."'

After winning 16-straight games at the beginning of the season, the Celtics have simply not resembled the same dominant squad.

"I don't think we're all that we were cracked up to be during our 16-game winning streak, and it's probably hit us more in the last month than it hit us before," Stevens said. "We have no excuses. I told our guys excuses are contagious. Everybody else has been playing too. ... At the end of the day, excuses are contagious -- go play.”

Luckily for Boston, their roster is ripe with versatility. Horford and Monroe can play both the four and the five. Morris can play the three or the four, as can Jayson Tatum. Jaylen Brown can play the two or the three. Both Marcus Smart and Terry Rozier can play either guard spot. That will allow Stevens to figure out the best combinations over their final 21 games.

Regaining early-season urgency

Earlier in the season, the Celtics emitted a certain swagger and confidence on the court. The wins were a byproduct of that attitude. Somewhere along the way, it faded, as evidenced by the recent comments made by Brown and Coach Stevens.

“I think we have a sense of urgency about ourselves. I think we understand the second half of the season and the importance of it, getting ready for playoffs,” Jaylen Brown said, per Ross Gienieczko of the Boston Herald. “You can see some of the older guys — Kyrie, Al (Horford) — the attention to detail, the stress about the little things is becoming more evident.”

“Toward the beginning of the season, everybody had that pop about them. We were quicker to the ball. We were more energetic, more enthused. We were faster, winning the foot races, things like that,” Brown noted.

Stevens understands the significance of playing with a constant sense of urgency on a nightly basis.

“We’re going to have to play with that kind of urgency,” he said. “These are things that prepare you for what you ultimately want to be a part of down the road.”

In order for Boston to re-gain their mojo and erase their downward trend, they’ll have to continue their two-game win streak and take care of business against the Memphis Grizzlies and Charlotte Hornets before squaring off against the Houston Rockets in what will be a statement game on March 3.

Overall, the Celtics seem slated to earn one of the two top seeds in the East, but if they expect to make it to the Finals, they’ll need to address the three concerns above.