The Dublin-born centre-back has already made 50 competitive appearances for the Hoops since his debut against St Mirren in September 2006.

O'Dea, 22, however, has asked to go out on loan until the turn of the year and has joined the Championship side in a loan deal until January 1.

O'Dea is determined to use his loan spell in England to gain the experience that he feels has prevented him from becoming a permanent first-team fixture at Parkhead.

"It's obviously great to sign a new deal but it's more important that I get out now and play football," he told the club's official website.

"This is a massive chance for me to go and play for a good club like Reading and prove my worth and then come back here and obviously try and do the same here.

"Brendan Rodgers, who is the manager at Reading, had tried to get me before when he was at Watford, and I know a lot about him. I've spoken to him and he's a great manager.

"I also know a couple of the Irish lads down there as well and they've had nothing but good things to say.

"So I know what I'm going into and I'm looking forward to getting started.

"I feel this is the right thing for me to do now - to play first-team football - and when I come back I never want to hear the word 'experience' said to me again.

"If I'm good enough to play here - and I think I am - this is the club I want to play for."

The Irishman added: "Tony Mowbray has been brilliant for me since he's come in.

"He's spoken honestly and done a lot for me. He thinks it will help me and, ultimately, it will help Celtic as well.

"He's been great and I owe a lot to him that this is happening to me.

"Even in the short space of time he's been here he's taught me a lot, along with the coaching staff, and he's someone I'd love to work under.

"I think this is the best way to do it now - to go out and play and then come back and be a part of his plans for years to come.

"Celtic have shown me how much they do want me, which is obviously good to know that but for me right now, I need to be playing, so this is for my benefit but also for the club's benefit as well."