Tottenham forward Son Heung-min is finally showing his true potential as he prepares to return to his former club in the Champions League, says Bayer Leverkusen boss Roger Schmidt.
The South Korea international joined Spurs from the Bundesliga side in a £22million deal in August 2015 and will now face them for the first time since leaving.
After struggling to hold down a starting spot in a mixed first season in England, Son has shone in 2016-17, scoring five goals in seven appearances - including the winner as Spurs defeated CSKA Moscow in their last Group E fixture.
Tottenham sit second in the group as a result of that win, one point clear of Leverkusen ahead of their meeting in Germany on Tuesday.
"After a tricky first campaign at Tottenham he's now showing his true potential and I hope that continues - with the possible exception of tomorrow night," Schmidt, who watched Spurs' win over Manchester City this month, said.
"We know what he's about. He spent a year here with me, he's a great player and a great person as well.
"I was privileged to coach [Son] at Leverkusen for a season. We have to keep an eye on every player, but from seeing the game at White Hart Lane, Son had an excellent game there."
Leverkusen's main threat is striker Javier Hernandez, who already has seven goals to his name this season including a strike in their 1-1 draw against Monaco last time out in Europe.
"The stats show that when he's had a chance to play, he scores goals," Schmidt said.
"Also consider that he has played for Manchester United and Real Madrid, two of the top teams in Europe, where there is stiff competition.
"Even then when coming on as sub, he has done well. Now that he has chance to play 90 minutes more, I think you can see he has more enjoyment in his game."
Schmidt added: "In terms of the Champions League, this is when it really gets going here at the BayArena.
"This is a stage where we can show what we can do. There is no better chance for us and no better opposition for us to show that against in this group."