Sunderland have agreed a deal to sign Fiorentina defender Marcos Alonso on loan for the rest of the season.

Alonso, who had a previous spell in the Premier League with Bolton, completed a medical with Sunderland on Monday and will officially join up with his new club when the January transfer window opens on New Year's Day.

The 23-year-old Spanish left-back will become boss Gus Poyet's first signing since he replaced Paolo Di Canio at the Stadium of Light in October.

"I can confirm Marcos is going to be with us for the rest of the season on loan from Fiorentina, which is something very important," Poyet said.

"I was looking for a player in that position on the left side and I hope he will help us and everybody will like him.

"I am delighted that everything is agreed."

Alonso began his career at Real Madrid before moving to England to join Bolton in 2010.

He spent three years at the Reebok Stadium, scoring five goals in 35 league games, before joining Fiorentina in July.

Alonso made just three appearances for the Serie A side in the first half of his maiden season in Italy and was told he would be allowed to leave in January.