Sean Dillon was paraded at Tannadice on Thursday

The 23-year-old has signed for the Scottish Premier League club until May 2009 and could make his debut against Rangers at the weekend.

United manager Craig Levein said: "He is a natural right-back and that is the position I wish him to play.

"But he also provides cover for both full-back positions."

Former Republic of Ireland Under-21 international Dillon, who had a spell with Aston Villa, moved to Shelbourne from Longford Town in January 2006.

"This is another good signing for the club," said Levein.

I see this as a big step up from playing in the League of Ireland Sean Dillon

"He's at the right age to develop, with his best years ahead of him and I'm sure that SPL football will allow him to keep on improving.

"Sean hasn't played competitive football since Shelbourne won the league some weeks ago, but he has kept fit and will be included in the squad for this Saturday's trip to Ibrox."

Dillon was looking forward to playing at a higher level.

"I see this as a big step up from playing in the League of Ireland, both on and off the park," he said.

"SPL football is very competitive and challenging and the facilities and stadia are very impressive.