Where will Celtics turn at center with Enes Kanter sidelined?

The Celtics new-look frontline took a hit on the depth chart Friday, as Brad Stevens ruled out starting center Enes Kanter with a knee contusion for both games this weekend against the Raptors and Knicks.

Kanter suffered the injury in the first half of Wednesday's opener after as a Sixers player slid into Kanter's legs. He will be re-evaluated early next week.

“I guess it was from the play in the first half where it looked like his knee buckled," Stevens said. "Probably could have been a lot worse but thankfully it wasn’t. He felt pretty good at halftime. He got checked at halftime but it stiffened up as the game went on and that’s why he didn’t go back in at the end of the game, the last six or seven minutes of the game.”

Kanter played well in the opener despite his injury, posting 12 points and 6 rebounds while helping to limit Joel Embiid to 15 points with solid post defense. The challenge gets tougher for the undersized C's tonight as they face a formidable Raptors frontline that features Marc Gasol, Pascal Siakam and Serge Ibaka.

“They’re great," Stevens said of the defending champs. "I think everybody forgets they were 17-5 without Kahwi. And if you watch them play in the preseason, they’ve been awesome. They went to Brooklyn and they looked great. They were good the other night. Probably not as good as the Brooklyn game. They’ve got a bunch of guys who play with great speed, they know what they’re supposed to do, they’re extreme competitors. They put heat on you on both ends of the floor for 48 minutes. It’s going to be really tough. It’s going to be a good second test of the season for us."

All of the C's remaining healthy centers are likely to get an opportunity on Friday night against the Raptors big frontcourt. The question now is where Brad Stevens will turn in the middle without his most experienced piece to start. A rundown of the options and how they match up against Toronto:

Rob Williams: The second-year big man looked solid in his season debut on Wednesday, posting four points and a couple rebounds and the only positive plus/minus on the roster in 12 minutes. He piled up four fouls though and his strength against a bigger piece like Gasol could be a problem in the interior. However, with so many athletic threats in the Raptors lineup, having a mobile shot-blocker like him in the fold could be a necessary boost for Boston's defense. Given that Ibaka plays backup center for Toronto, there won't be an easy matchup for Williams with either the starters or the bench from a defensive standpoint, so playing him with more talent in the starting five may be a better way to hide him on the offensive end. Either way, he's going to have to stay disciplined and not bite on perimeter shot fakes against the Raptors' capable 3-point shooters.

Daniel Theis: This is the safer choice from a defensive perspective for Stevens. He is giving up a few inches to Gasol but knows how the big man plays after several head-to-head battles over the past few years. Theis will also pull Gasol out of the paint more with his 3-point shooting ability, something that should help open up the paint for the rest of the starting five. The third-year center played just 10 minutes in the opener against Philly in what was a tough matchup for him with Embiid, but I'd expect that number to at least double tonight. He has a good sense of the C's defensive schemes and that will be important against a high-powered offense like Toronto. He can get bullied in the post by Gasol and Ibaka though so that's an area to watch.

Vincent Poirier: The French rookie got a DNP-CD in the opener but is probably the best matchup for Gasol from a size/strength standpoint out of everyone at center. He finished the preseason at No. 4 on the depth chart though for a reason even though he looked solid in his limited exhibition game minutes. There is no guarantee that he will see meaningful minutes, but the Raptors are just the type of team the C's signed him to match up with. Given that both Williams and Theis can be prone to foul trouble, it wouldn't be a shock to see him forced into action early in this one.

Verdict: If Stevens wants to gamble, Williams will be the choice here to give him some minutes with a starting five that can better cover up his offensive limitations. However, Theis has to be considered the favorite based on his preseason and familiarity with the schemes. It's going to be a stiff challenge either way against an impressive Raptors team that posted over 130 points in their regular-season opener on Tuesday night. Boston's defense sprung some holes in the second half against the Sixers on Wednesday night and will need to better tonight to get in the win column.