"They were all very important stages in my career," he said. "Before Bolton I played for Real Madrid and I was getting involved in the first-team training since I was 16 and then I played with the first team at 18.
"Bolton was another important stage for me. I learned a lot, even if I didn't fight for any titles. We were not too close, only one semi-final of the FA Cup and then I went to Sunderland for only four or five months and we fought relegation.
"At the end of the day we did a very good second half and we played in the final of the (2016 League) Cup.
"That was all very important for me to be the footballer I am today. You learn more when it's hard than when it's easy.
"I'm very happy about my career, and I'm proud of having played in Bolton and Sunderland. Still today I follow them and want what's best for them.
"That makes you enjoy the good moments even more and fight to keep playing for a good team and keep playing for titles and not fighting for relegation.
"It was perfect for me to improve as a player and to learn. I'm very happy with my career."