By Matthew Geagan, CBS Boston

BOSTON (CBS) — Smallball is returning to the Celtics starting lineup. Not because Brad Stevens is ditching the two-big lineup that has been a disappointment thus far, but because the head coach really doesn’t have any other choice.

With Robert Williams reportedly testing positive for COVID-19, and Tristan Thompson and Grant Williams out due to contact tracing, the Boston frontcourt is going to be extremely limited over the next seven days. Unless Stevens really wants to get nuts and start Daniel Theis and Tacko Fall, that double-big lineup ain’t happening again until that trio of bigs returns.

That isn’t the worst news for the Celtics. The two-big lineup that features Thompson and Daniel Theis hasn’t had the desired effect over the first nine games of the season, with that pair of bigs sporting a minus-18.1 net rating in their 97 minutes on the floor together. It’s not great.

And now Stevens will have to put the experiment on hold, and hope that he’s got enough size left elsewhere on the roster. Theis is still around to start, but losing that trio for a week leaves him with just Fall on the bench as a backup big. Granted, Fall is big enough to account for a pair of bigs, but he’s still an extremely raw NBA player.

Instead, the Celtics are going to have to go back to the smallball that is dominating in the NBA. Normally we’d expect Grant Williams to be joining the starting five in such situations, but he’ll be playing board games on his own for the next week. So it could be Semi Ojeleye joining Marcus Smart, Jaylen Brown, Jayson Tatum and Theis in the Boston starting five.

Here’s how the rest of Boston’s depth chart looks at the moment: Guards Payton Pritchard, Jeff Teague, Javonte Green (fresh off his own quarantine), Carsen Edwards and Tremont Waters, and forward Aaron Nesmith. Fall is the only big off the bench.

Expect to see a lot of Semi and Tacko over the next seven days. We also won’t rule out Pritchard making an appearance at center, because the rookie can seemingly do everything else in the NBA.

It’s unclear when Boston’s trio of bigs officially entered quarantine, but it’s safe to assume they likely won’t be back until next Friday against the Orlando Magic at the earliest. They will potentially miss four games over that stretch: Friday against the Wizards, Sunday against the Miami Heat, Monday against the Bulls in Chicago and Wednesday against the Magic. A Friday return in Boston’s second straight game against Orlando could be overly optimistic too, should Thompson or Grant Williams also end up testing positive.

And now the Celtics have to worry about more COVID cases popping up elsewhere on the roster. Given that they had players test positive after the team was on a seven-day road trip, they’ll be lucky if no additional players test positive in the coming days.

Things could get really tricky for the Celtics in the coming weeks.