There are a number of givens as the Celtics embark on their 65th season as an NBA franchise.

Paul Pierce will score 20 a game and remain the go-to guy down the stretch. Ray Allen will hit 35-40 percent of his 3-pointers. Rajon Rondo will average a double-double and will make at least one opponent look stupid every game. And when he's healthy, Kendrick Perkins will still manage to rack up 10 technical fouls before the season's over — most of them for giving the refs a look like he just smelled Shaquille O'Neal's jockstrap.

In other words, the mainstays of the past two seasons will remain the mainstays.

There is far more doubt this Media Day Monday, however, about three of the keys to the Celts' 2010-11 campaign: defense, rebounding and the bench.

The defense, for one, has lost three of its more significant contributors: Perk, Tony Allen and coach Tom Thibodeau. Perk has been replaced by the bigger but slower Shaquille O'Neal; Tony by  an injury-prone Marquis Daniels; and Thibodeau by Lawrence Frank, who many believe is being groomed to replace Doc Rivers.

Not much else needs to be said about the rebounding: The Celtics were 29th in total rebounds during the regular season on their way to finishing 25th in rebounding differential (-1.5). Watch the fourth quarter of Game 7 of the NBA Finals to understand why that's a sore spot for the Celtics, then take into account for a second time that Boston has lost Perk for the first half of the season.

And the bench? A concern mostly because it's heavy on newcomers: Eight of the 11 players currently on the depth chart did not suit up for the Celtics last season.

Those worries leave four X-factors heading down to Newport, R.I., for Celtics training camp.

The return of 'Quis
Daniels came to Boston in 2009 with high hopes after a career season in Indiana of 13.6 points, 4.6 rebounds and better than a steal per game. Disappointment would be putting what came next lightly –  the 29-year-old played in just 51 games, hampered by injuries and a jump shot that suddenly looked awful.

With T.A. now in Memphis, Daniels becomes the first guy off the bench when Pierce needs a blow. Danny Ainge, for one, proved his confidence in Daniels by opting not to seek another swingman in free agency.

"We know what Marquis is capable of doing," Ainge said last week. "Last year, when he came back [from a thumb injury], we had brought in [Michael] Finley and Nate [Robinson], and it was tough for any of those guys to get in a full rhythm because they were all sharing minutes. We know [Marquis] can play."

The Other O'Neal
I consider the other O'Neal — Shaq — to be a given: 15-20 minutes a night, 10 points, five boards, 0-for-5, .000 from the free-throw line and a whole lot of hoopla.

Jermaine O'Neal is more of a wild card. The guy can swing from a 25-point, nine-rebound night in March to an embarrassing playoff performance just a week later against Boston. He's that kid you played with in high school who would've been 10 times better had he just laced up his sneakers and tried.

If Doc and Kevin Garnett can get him to do that (and they might be the only ones who can), he'll start over Shaq and could help shore up the defensive and rebounding deficiencies. If not, Semih Erden will be seeing a lot more time on the floor. And that's bad news for the Celtics.

The rookies, namely a former Longhorn
Yes, I like Luke Harangody, too, but he's buried behind both O'Neals, Glen Davis and Erden in the paint positions and likely won't see much time at the 3.

Avery Bradley, on the other hand, could be vital as a defensive replacement, especially down the stretch of the season and into the playoffs. Perhaps nothing was more important in the Celtics-Lakers Finals than Boston's ability to contain Kobe Bryant. The No. 19 pick, Bradley, could be the guy to take over those duties — and unlike Tony Allen, he's got a jumper.

If Bradley can heal well from ankle surgery (and Ainge said last week Bradley should be ready by the start of the season), he could double as the third-stringer at both point and shooting guard.

The Big Knee
The C's went 4-6 last season when Kevin Garnett had to sit out with a hyperextended knee. When the Big Ticket's knee was at its best (during the postseason), they almost ran the table in a tournament that no one had them winning.

Word is, heading into Garnett's 16th NBA season, that problem knee is fully healed.

"I think Kevin needed some rest, some time off, and he took it, but he's ready for camp," Ainge told reporters. "He's in much better shape than he was last year in training camp. I think that K.G. got better as the year went on last season, and we saw him moving much better in the playoffs than in the regular season."

He, alongside the two O'Neals, will be the key cog in Boston's efforts on defense and the boards.

A lot will need to go right for the Celtics this year. Big Baby and Delonte West need to stay out of trouble, Perk needs to come back at full strength and Pierce and Ray Allen also must stay healthy as they venture further into their 30’s.

It’s a lot to ask for, but it is worth noting that the Celtics thrived as the underdog in 2010. Perhaps it would be unwise to tell them they can’t do it again.