PORTLAND, Ore. -- Because of a concussion he suffered Monday in practice, Dallas Mavericks center Chris Kaman might miss all four games on his team's current four-game road trip.Kaman is out indefinitely after he fell on the floor and banged his head during Monday's practice at American Airlines Center. He also has to pass the NBA's stringent rules in regards to concussions before he can return to the court."He'll be back when his symptoms abate and we don't know a timetable for it," coach Rick Carlisle said. "I don't think it's that serious, but these things, you've got to be very careful with."There's a test, and every NBA player takes a baseline test before the season so that they have a comparison. At such time that he is able to pass that test, then he'll be cleared."Kaman is averaging 12.4 points and 6.2 rebounds in 23.7 minutes. But he recently was taken out of the starting lineup after starting 33 of the Mavs' first 42 games."We're definitely going to miss him, but we've got a lot of other guys that can step up and play big-time ball for us," point guard Darren Collison said. "We're going to miss his scoring and just his presence on the court."I wish him the best, and he'll be fine when he gets back."Asked how Kaman suffered the concussion, Carlisle said: "It doesn't matter. There was a collision, he fell down and bumped [his head] on the floor."Last year center Brandan Wright suffered a concussion and missed six games from March 3-12 after going through the NBA's battery of tests. In the Mavs' case, at least they have Elton Brand, Bernard James and Wright to lean on while Kaman is sidelined.And if the Mavs decide to go small, Carlisle noted he'll use Shawn Marion at the center position."We're all going to step up and help each other more," Marion said. "We're deep, but everybody's got to step up because that's another big body for us."It's not like we've got 7-footers growing on trees."A solid benchThe Mavs' bench has been on a tear lately, scoring 56 points in Sunday's 110-95 win over the Phoenix Suns and ranking third in the NBA.But how does it stack up against the Mavs' bench that was so effective during the 2010-11 championship season?"Every team is structured a little different," Rick Carlisle said."In '11 we had some pretty good players on that bench."The Mavs' bench in their 2010-11 season included Jason Terry, J.J. Barea, Brendan Haywood, Ian Mahinmi, Peja Stojakovic, Corey Brewer and, at times, Shawn Marion.