Selles was allowed to come off contract by Saints following their relegation.
“After the game against Brighton (21 May) they called me in for a meeting the next day and told me they wanted to go in a different direction," he told Tipsbladet.
“I respect that and it's the club's decision. I would have liked to have stayed and continued with the project because I now know everything in Southampton.
“I know the players, what personnel we need for the coaching staff, the environment and the country. But again, it's not my decision. They made a different decision and I respect that."
Selles added: “When I was manager, I decided through a verbal agreement with them that I wouldn't go back. At that time, I needed to invest everything in the position of manager.
“I don't do anything by halves or be protective of myself. I also try not to have a plan in case something doesn't work out. I wanted to send a signal that I was fully invested in the job as a manager.
“It was not possible for me to do it in other ways, and therefore it is not possible to continue as an assistant next season.
"I've already spoken to clubs in England and Spain. Let's see who is interested in talking to me and starting a project together."