AIDEN O'Brien says he cannot wait to play regular first-team football after completing a loan move to Crawley Town until the end of the season.
The Red Devils made an approach for the 19-year-old after he scored two goals on his debut for the Republic of Ireland U21s against the Netherlands last week.
And the Islington-born youngster, who signed his first professional contract at The Den on his 17th birthday, admitted he jumped at the chance to move to the Broadfield Stadium.
O'Brien told NewsAtDen: "I was over the moon when I heard Crawley wanted to sign me. I was a bit shocked to be honest because I haven't had the best of seasons.
"Playing for the national team has helped me a lot. The main thing for me is to get some experience and play first-team football. Hopefully I'll score a few goals as well.
"I had a quick meeting with Kenny Jackett and Scott Fitzgerald the other day and they both said this would be a really good move for me.
"They want me to go out there and do my best, and hopefully I'll be ready for the first-team when I get back. My ambition is to make it as a professional at Millwall.
"I've been on loan to Hayes & Yeading and Staines before but this will be a whole different set-up – Crawley are in League One fighting for the play-offs so I'm really excited."
O'Brien's performance for the Ireland U21s undoubtedly fast-tracked his move to Crawley, but the striker was just as pleased that Fitzgerald, the club's head of youth, had been there to watch him.
"It was great that Scott was at the game – it made me feel really wanted," he said. "Millwall have been so good to me since I started playing for the U15s.
"It must have been the biggest game of my career so far, definitely. The U21s is a really big stage so I had to impress and I'm glad my preparation paid off.
"I found that international football is much different to club football. The tactics are more about the other team and how to defeat them, whereas at club level you have your own style of play.
"I was playing against some really good players so just starting the game was a big achievement for me. Getting two goals against a big country like the Netherlands has boosted my confidence."