Andre Schurrle has claimed that he did not have the trust of Chelsea boss Jose Mourinho during his time at Stamford Bridge.
The 24-year-old Germany international was sold to Wolfsburg for £24 million in January on the day Juan Cuadrado arrived in west London.
And now the World Cup winner has said a breakdown between him and Mourinho played a part in his return to the Bundesliga.
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According to the Times, Schurrle said: "I had a good time at Chelsea and was accepted in the team, so it's difficult to explain why I left.
"My performances were good as well, but there was a time in my second season when I felt I didn't have the manager's trust anymore and I didn't play many matches from the start.
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"I don't know why Mourinho didn't trust me. It all felt a bit weird to me."
Schurrle's time at Stamford Bridge lasted just 18 months, scoring 14 goals in 64 appearances, including the goal which sparked a second-leg comeback in the Champions League against Paris Saint-Germain at Stamford Bridge in April 2014.
Chelsea won the match 2-0 and progressed to the semi-finals on away goals.
"I started a few games, was on the bench for a few, then started some more. It was up and down the whole time.
"I had a lot of good talks with the manager and respect him a lot, as he told me to my face what he wanted me to do.
"I had some very good games, but there was often an ordinary game soon afterwards as well."
It is clear that Mourinho does have respect for Schurrle, however. The Portuguese texted his former player after the Blues won the Premier League title in May, inviting Schurrle to the final game of the season to receive his Premier League medal.
Schurrle was eligible for a medal having played the required five league matches before his departure.
The Wolfsburg winger also spoke about the seemingly impossible task of a youth player forcing his way into the first-team squad.
"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 said.
The former Bayer Leverkusen player then spoke highly of Eden Hazard, suggesting he is a favourite of Mourinho's.
"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 Juan Mata, occasionally Kevin 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."