The promising starlet got a chance in the Europa League in midweek against Galatasaray.
Despite getting his first goal for the club, Lankshear ended the night on a bad note by being sent off.
Speaking after the 3-2 defeat, Postecoglou stated: “Yeah, look Will took his goal well, he worked hard for the team. Obviously he hasn't had a lot of experience at senior football so he would have learnt a lot today.
“The red card, it was a bit of overenthusiasm in that moment to give away a foul, but he'll learn from that. The same with Lucas (Bergvall) here. Giving him an understanding of the levels here. It is not easy when you are playing away in Europe.
“You can only allow them to learn that by exposing them to it. I thought Archie (Gray) was great. It was a tough game for us defensively at different times but I think we'll get so much growth out of him because he's not playing in his position. I guess for three teenagers in the starting line-up, I think they'll learn a lot from it and hopefully it helps with their development.”