The Celtics approached Thursday's NBA trade deadline with a glaring need for an additional big man. They didn't add one, and actually, they had to deal away their first big off the bench to get necessary guard help. You can do the math. "We can't get into foul trouble," Celtics coach Doc Rivers joked while addressing his team's lack of frontcourt depth after sending Jason Collins to Washington with injured Leandro Barbosa in exchange for third-year guard Jordan Crawford. Boston is dangerously thin up front with Kevin Garnett and Brandon Bass being backed up by a group that includes Jeff Green, Chris Wilcox and Fab Melo. And Rivers admitted his team's available bigs could further dwindle at times before the end of this road trip. "Listen, I'm going to sit Kevin in games, and, so, those are the games it'll be an issue for us. We'll be really small," said Rivers. "We may have to add a D-League guy, [because] I would be surprised if Kevin played all three of these games coming up. That puts a lot of pressure on us. But it's what we're going to have to do."