Shortly after Glenn Robinson III signed with the Pacers in July 2015, team President Larry Bird gave him an important assignment: make Paul George work for shots in practice.

Robinson pored over video of George until he memorized George’s every on-court tendency. Within weeks of arriving in Indianapolis, Robinson had impressed enough for the Pacers to name him George’s backup and scrap plans to send him to their Development League (now G League) affiliate.

Four years later, Robinson considers those practice duels with George a driving force behind his NBA longevity. They taught Robinson that, in a league loaded with prolific wing scorers, he needs only to make life difficult on his man — not necessarily shut him down.

That’s all the Warriors will ask of Robinson this season as he tries to help fill a defensive void. With Kevin Durant, Andre Iguodala and Alfonzo McKinnie gone, and Klay Thompson out until after the All-Star break with a torn ACL, Robinson might be Golden State’s most proven perimeter defender not named Draymond Green.

Though Robinson can cut to the rim, knock down open jumpers and feed Stephen Curry on dribble-handoffs, the Warriors signed him in July largely for his reputation as an on-ball stopper. His long arms, lateral quickness and encyclopedic knowledge of All-Stars’ go-to moves could go a long way in determining whether Golden State remains at least an above-average defensive team.

“I think the first couple days, he was kind of figuring out how we do things on that side of the ball,” Green said. “But as time went on, he got more and more comfortable. I think he could really help us defensively. He has all the tools.”

With Curry and D’Angelo Russell leading the offense, the Warriors should still hang gaudy point totals. The question is whether their defense will hold up enough for them to contend for a playoff berth until Thompson returns. In addition to being one of the greatest shooters in NBA history, Thompson is one of the league’s elite perimeter defenders.

Thompson’s size, endurance and basketball IQ have long made him a daunting matchup for everyone from LeBron James to James Harden to Russell Westbrook. With Thompson likely out until March, the Warriors will replace him in the starting lineup with Russell — a so-so defender on a good day.

In his 99 preseason minutes, Russell posted a defensive rating of 118.8, which ranked 514th out of 549 NBA players. No longer can Golden State consistently hide Curry on the opponent’s worst scorer.

With Green plenty busy organizing the defense and quelling the league’s many potent big men, Robinson will be asked to guard the likes of James, Jimmy Butler and Giannis Antetokounmpo. His first big test comes Thursday, when he’ll match up with reigning Finals MVP Kawhi Leonard, now with the Clippers, in the Warriors’ season opener.

“I think the team definitely needs a guy to step up and be that perimeter defender, especially with the talented wings coming in,” said Robinson, who was named Golden State’s starting small forward last week. “I’m excited to show what I can do. As you can see, it can make you a lot of money if you can do it.”

As a sophomore at Michigan, Robinson began to recognize that, thanks to a 6-foot-9 wingspan, he could be more than a spot-up shooter and award-winning dunker. In the lead-up to the 2014 NBA Draft, the Wolverines’ assistant coaches took him through a gantlet of drills geared toward everything from powering through screens to sliding his feet.

During his three seasons with the Pacers (2015-18), Robinson made a habit of steals and deflections. His sound defense on pull-up jumpers was a big reason Indiana ranked among the league’s top teams annually in opponents’ 3-point percentage.

Though Robinson struggled offensively with the Pistons last season, he posted a defensive rating of 99.1 in limited minutes over the final three-plus months. That would have led the Warriors, who didn’t have a player finish the year with a defensive rating better than 104.3.

In recent weeks, Robinson has studied video of Thompson, trying to emulate the player he will try to replace.

“The good thing is, he’s been in the league for a while now, so he generally knows players,” Warriors head coach Steve Kerr said of Robinson, who can still recite George’s on-court tendencies on cue. “He has a scouting report on different players, and he’s felt what it’s like to go against them.”

Connor Letourneau is a San Francisco Chronicle staff writer. Email: cletourneau@sfchronicle.com Twitter: @Con_Chron