Xavier has made 20 appearances for Boro this season

The 34-year-old former Portugal defender rejoined Boro in 2006 following a drugs ban having originally signed for the club in August 2005.

Boss Gareth Southgate told the club's website: "We have been unable to give Abel the terms he was looking for."

Xavier insisted the split was amicable, telling the club's website: "Gareth has my respect as a person and as a coach."

606: DEBATE Should Boro have tried harder to keep Xavier?

Xavier said he believed Middlesbrough would progress under Southgate because of the respect the players had for him.

"That is a great quality because most of the time this does not happen with players that become managers, as they lose respect towards the players," he said.

"When this kind of thing is missing the players do not show respect to the manager but this is not the case with Gareth."

Southgate said "I am disappointed Abel has decided not to stay with us but I'd like to thank him for his contribution to the club.

"He always did well when called upon and we wish him all the best."