"My performances were good... but there was a time in my second season when I felt I didn't have the manager's trust any more, and didn't play many matches from the start," Schurrle, who scored 11 league goals for Chelsea, told the Times.
"I don't know why Mourinho didn't trust me. It all felt a bit weird to me. I started a few games, was on the bench for a few, then started some more."
The 24-year-old said his inability to secure a regular starting berth under Mourinho resulted in him failing to produce his best football.
"It was up and down the whole time. I didn't get any consistency from the manager so found it hard to produce my best," Schurrle said.
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"That's probably the biggest reason I wanted to leave."
The former Bayer Leverkusen midfielder said Eden Hazard's form for the champions had made it difficult for other wingers to break into the first team.
Juan Mata, Kevin de Bruyne, Mohamed Salah and Juan Cuadrado have all left Chelsea since January 2014, a trend that Schurrle partially attributed to Hazard's sustained excellence.
"It's difficult for young players at Chelsea because they're a big team with big stars. It's not easy to play every match," he added.
"It's even harder for the wingers as there are only two in the team and Eden plays always, as he's the best player in the league.
"So you have one position on the right wing which was between Willian, Oscar, myself, sometimes Mata, occasionally De Bruyne.
"The other thing is that Eden is given more freedom so the other winger has to work even harder. You have to work for that freedom, and Eden deserves it as he creates everything up front.
"He scores goals and makes assists so it's right he should have that freedom."
(Reporting by Shravanth Vijayakumar in Bengaluru; editing by Sudipto Ganguly)
