"I'm very impressed," Lehmann said. "The advantage of being a goalkeeper is that most of the time you only have to react, whereas an outfield player has to act.
"In his position he needs to chase young people, quick people.
"It's quite impressive, I have to ask him how he does it."
While Weir is at one end of the age spectrum, his possible partner in central defence is at the other extreme.
Danny Wilson, 17, has started the last four games for Rangers including the Champions League draw against Unirea Urziceni in Bucharest.
The teenager could continue against Stuttgart after Madjid Bougherra, who has not played for Rangers since September through illness, injury and late arrival from international duty, again showed up behind schedule from his exertions with Algeria.
Lehmann said: "I just thought, my son is 13 so it's a bit strange.
"But it's a compliment for him to be picked by a big club like Glasgow Rangers and in a great competition like this.
"I just kept on playing, that's why I can face him."
Lehmann plans to retire at the end of the season but he insisted the pressure of Stuttgart's poor domestic form would only bring the best out in him.
However, he admitted he was glad to face a team who are in greater need of points as Rangers bid to move off the bottom of Group G.
"They are a bit more under pressure than us," the former Arsenal player said.
"They need to come out for the win. In recent games we've been playing opponents who are quite defensive and just want to get a result, so this game could be a bit different."
Rangers v VfB Stuttgart 1st Goalscorer: Weir, D. 33/1