While the Spain international also admits that the Blues’ back-up goalkeeper Kepa Arrizabalaga helped persuade him to move to London.
The European champions will pay £3.5m for a season-long loan, while there is also an option to make the move permanent for around £30m.
“I spoke with (Diego) Simeone,” Saul told Spanish streamer Ibai Llanos on Twitch. “I have been playing in different positions for three seasons.
“I owe everything to Diego and he must be selfish and think of the group.
“I saw myself stuck in a position that was not mine. Chelsea’s option was to get out of the comfort zone, a challenge. I asked Simeone and Miguel Angel to train in my position.
“I understand that he refused and from there they decided this. I’ve been here since I was 13 and it’s very hard.
“I want to take up other movements and positions that I did not perform from the other position. It is the most important reason for my decision.”
Saul knows Kepa well from their time together with the Spanish national team and he revealed his presence at Chelsea made the decision easier to accept the new challenge.
“It is very important that he be there. It is an important step,” Saul added. “If he had not been there, it would have been different.
“Going on loan for a year and having a partner with whom I have been spending many years in the lower categories of the National Team is important.”
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