NEWPORT (AP) - Boston Celtics coach Doc Rivers canceled training camp practice scheduled for Monday, saying he wants to give the defending NBA champions a day off before they prepare for their first preseason game.

Boston takes on the Philadelphia 76ers on Wednesday at the University of Massachusetts' flagship campus in Amherst.

"I liked the way we were going so I figured go one more day, give them a day off and then we get a day before our (first) preseason game," Rivers said Sunday after the Celtics held their final practice at Salve Regina University. "It works out pretty good."

Rivers says he was pleasantly surprised by what he has seen of rookie Billy Walker.

"He's not your typical rookie that thinks he's got it figured out already," Rivers said. "He really isn't. He knows he has some catching up to do but he's been a pleasant surprise."

The 6-foot-6, 220-pound Walker was the 46th overall pick by Washington in the 2008 NBA draft but was acquired by Boston in a straight cash deal.

He averaged 15.3 points in just 37 career games at Kansas State and played only six during the 2006-07 season after tearing his left anterior cruciate ligament.

"Clearly, he would have gone earlier if he projected healthy," Rivers said. "I think he would have been mid-first (round) definitely to low-first. But everyone was scared about his knee."

"He clearly can earn a position if a team is willing to take the chance."

The question is what position can he play since, considering his height, he's a classic "tweener."

"He's that in size but in body he's a three," Rivers said. "I think he would struggle even more guarding twos. He's athletic enough to, but his body tells you he's a 3 because he's so strong.

"He attacks the basket, too, and will live on the foul line. He's got to work on his ball handling a little bit, but if he comes off the cuts, he's going to live on the foul line."

If that transpires, Walker may prove to be an asset especially if he can improve his free throw shooting. In college he shot 72.7 percent which is adequate but not spectacular.

Rivers says he believes that Walker could excel in a transition game and could be even more productive as a post-up guard.

"Billy's great in transition," Rivers said. "But I think Billy's going to be a great post guard. I don't know if he knows that yet, but I think he will be."