The United States international has recently returned from a serious ankle injury, which he sustained at Forest near the end of his loan spell from MLS ahead of the 2001 US season.
Olsen became a huge fan favourite at the City Ground during his time in England, and nearly signed permanent terms, only for Forest to fall short of MLS' reported asking price of $2.5m.
Four operations later, Olsen has finally made it back on the pitch for United, with his fitness levels growing by the week.
And, while his focus is clearly set on making it back into the US national team, the 25-year-old has never forgotten the 'lessons' he learned from his short spell in the First Division.
"I had no idea what to expect from the fans at Forest and was very surprised that some of them took to me and my play," said Olsen.
"If I could take this opportunity to thank them for giving me an experience that I will cherish.
"Someone said to me the other day what a shame it was that I went on loan and got injured," he added.
"I told them I do not only not regret going to Forest, but I don't even regret the injury because it came about because I gave the fans what they deserved, everything I had.
"The fans at Forest taught me a lot about passion and, for that, I will never forget my time there."
Indeed, Olsen wants to return to Nottingham at the end of the current MLS season, which ends in October, if not sooner for the winger, should United fail to make the play-offs.
"Whether it's not a loan or just training, that's fine," Olsen told The Northern Virginia Journal.
"Wherever I can get a sniff. I think that would be okay if I wanted to go back to Nottingham, just to train."
Should Olsen head to England before the start of next year he will not be able to play competitive football, due to the transfer and loan window being closed until January 1.
However, he still wants to explore what his possibilities are with Forest.
He added: "I don't even know if I can get my work permit right now, being out of the national team for so long.
"So maybe if I can get over and train a little bit somewhere, it would be good, because I've had a little bit of a pseudo-season with only four or five games, probably eight in the end. I need to get fit."
Olsen could begin his loan with Forest in January, with the new MLS season not kicking off until late Spring, and his work permit concerns would be allayed by the fact that the Home Office would ask US national team manager Bruce Arena for a statement to confirm Olsen would have been part of the States' set-up at the time he was out injured.
That would make up the required quota of 75 per cent from his last 24 months of international matches.
DC United manager Ray Hudson will also support Olsen's mission of returning to Nottingham, with the Newcastle-born boss noting the need for his continued progress back to full fitness ahead of the midfielder's final year of his current MLS contract.
"Even if it's just in a practising environment, if he's not going to play, if he can get back to Nottingham or one of the clubs back home, or in Germany - we've got some good relationships with clubs back in Europe," said Hudson.
"I'd be delighted to let him go. He's still building his stamina up."
One question that still remains is whether Paul Hart, currently at the helm of Forest, would be willing to put faith in a player who impressed the previous management at the club, and an issue he has been trying to distance himself from.
Allowing Olsen to prove his worth in training could see Hart having his own interest in adding the American to his squad for the winter months, as Forest try to push for a play-off position come the end of the season.
