Fox, the fifth pick of this year's draft, played only seven minutes in the Kings' 83-76 loss to the Dallas Mavericks in Las Vegas, with 0 points and three assists. He was benched before the start of the second quarter because of his ankle, which he originally injured in Monday's game against the Los Angeles Lakers.
Fox also sat out Wednesday's win over the Milwaukee Bucks but decided to give it a go against the Mavs. Kings summer league coach Jason March said he decided to cut Fox's night short as a precaution after Fox told him the ankle "didn't feel right."
"You're talking about a guy who wants to play every time he can get on the floor, and he wanted to play tonight, so we let him go," March said. "I took him out and he took his shoe off and was trying to do something with his shoe and said he was ready to go. He went back and said he didn't feel right, and I said, 'You're done.'
"It's nothing serious. Just didn't feel 100 percent. Didn't want him to be out there and risk anything."
Meanwhile, Smith scored a team-high 25 points, including 15 in the first half. He added seven rebounds, two assists and three steals.
The Kings play the Phoenix Suns on Friday.