And, after seeing Ronaldo score in both legs of the last-16 encounter, Wellenreuther came out knowing he was facing the best in the world.
"Playing against Cristiano Ronaldo was something very special,” he told Goal and SPOX.
“For me, he is the best player in the world. His runs and his power are incredible.
“Also in the games against me, you have unfortunately seen that he is freezing cold and always on the spot. Although I saved some balls off of him, in the end he scored twice.”
Wellenreuther isn’t the only goalkeeper to finish a Champions League game against Ronaldo frustrated as the Portuguese is the top scorer in the competition’s history with 126 goals.
The 23-year-old is now playing in the Eredivisie with Willem II, but sees himself returning to play in the Champions League one day.
"Once you've played Champions League, you'll want to go there again someday,” he explained.
“The Champions League is like a drug. So I hope that I can continue my hard work and that in the next few years there will be some more international games.”
Wellenreuther joined the Dutch club in the summer of 2017, and this season helped them reach the final of the Dutch Cup after he saved three out of five penalties in the semi-final shootout.
"I am German and have always dreamed of playing in the Bundesliga,” he said.
“Nothing has changed to this day. It is one of the best leagues in the world.”
As a 19-year-old in 2015, Wellenreuther was sent out on loan by Schalke to Segunda División side Mallorca to aid his development.
And, following his experience in Spain, Wellenreuther is open to the idea of playing all across Europe.
"Especially the Premier League has a tremendous appeal,” he explained.
“I do not know a player who cannot imagine playing there someday. After gaining experience in La Liga 2, I also know how strong and attractive La Liga is.
“Ultimately, it depends on whether you feel comfortable in the whole club, you believe that you can achieve something together. That is definitely the case in the Netherlands at the moment."