MANCHESTER, England (REUTERS) - Manchester United have reached an agreement to sign promising young defender Guillermo Varela from Uruguay's Club Atletico Penarol, the Premier League champions said on Friday.

The 20-year-old Uruguayan, who joins for an undisclosed fee, is the first signing under new manager David Moyes who has taken over from retired Alex Ferguson.

"Guillermo will immediately join up with the Uruguay Under-20 squad for the upcoming FIFA Under 20 World Championships in Turkey," United said in a statement on their website (www.manutd.com).

Varela, who has been training with the United first team in recent weeks, is a full-back who plays on the right flank.