France will play next on Friday against Argentina, who advanced by defeating Serbia on Tuesday night.
Walker arrived in China as one of only two All-Stars on the US team - the other being Bucks guard Khris Middleton - and he did an excellent job in helping to advance the team to the quarterfinals with a 5-0 mark.
"Any loss hurts. In this situation, it hurts more", Popovich said.
The U.S. had won 58 consecutive tournament games in FIBA and Olympic competition, starting with the bronze-medal game at the 2006 world championships and continuing through every FIBA Americas, World Cup and Olympics event since.
Rudy Gobert (21 PTS & 16 REB) and France upset Team USA 89-79 to advance to the @FIBAWC semi-finals! The Americans were abused in the pick and roll by French ball-handlers Fournier and Nando De Colo (18 points), along with Gobert, and their ill-preparedness for that scenario - both by roster-building and execution - cost them a medal. France switched at almost every opportunity from its point guard to power forward.
Mitchell's scoring production fell off in the fourth quarter.
'It doesn't mean anything if you don't win in the end, ' Gobert said. He tallied just two shot attempts in the fourth, and his second attempt came with Team USA down 10 in the final 10 seconds.
Though Team USA lost, players showed growth throughout the tournament. Marcus Smart made three free throws after getting fouled by Gobert to put the US back on top, and the Americans took a 66-63 lead into the fourth.
Donovan Mitchell provided an antidote to France's imposing defense, at least for the first three quarters of Wednesday's contest. He led all scorers with 29 points on 12-of-23 shooting and 3-of-6 from deep. Celtics forward Jayson Tatum missed the game with an ankle injury.
Popovich had the highest praise for France and coach Vincent Collet. Spain awaits the victor of Wednesday's Australia-Czech Republic game in the other semifinal. France deployed Knicks point guard and defensive ace Frank Ntilikina throughout the fourth alongside Gobert, and Nicolas Batum provided necessary length and switchability in the final minutes.
Team USA and the Czech Republic face quick turnarounds, as they will play again on Thursday in the classification bracket.