The Netherlands international struggled to make any sort of impact during his maiden campaign in North London, scoring twice in the Premier League upon joining from AZ.
Janssen's future looked bleak heading into the 2017-18 campaign, with Fernando Llorente being brought in from Swansea City to provide competition for Harry Kane, and the 23-year-old decided it would be best to reignite his career at Fenerbahce.
After seeing the striker net his first goal for Fener on Sunday, Pochettino told reporters: "I think it's important for him [to score] because always all the players struggle in their first season in England.
"When you come from Netherlands it's a different level of competition and in the end he wanted to leave and he decided to go to Turkey, and we wish him all the best and we are happy he scored. It was really good for him, to try to again build his confidence.
"Here he sometimes played, sometimes didn't play. But you know when you have Harry Kane in your position it's not easy to fight and be motivated every day to try to give your best. It was his decision, with the club's decision, to send him on loan but we hope he starts to build his confidence and trust and scores goals."
Janssen turned down the chance to stay in the Premier League with Brighton & Hove Albion, rejecting the Seagulls' deadline-day approach.