AITOR KARANKA has invited former team-mate Pablo Mastroeni to work with him at Middlesbrough for a few days, sparking suggestions the Colorado Rapids head coach could be in line to replace Craig Hignett on the Riverside coaching staff.

Mastroeni, who only took up his first managerial post in January, has travelled to Teesside with the blessing of his MLS employers, who finished eighth in last year’s Major League Soccer.

However, with the new MLS season not due to begin until March, sources in the United States have claimed that Mastroeni’s position is in doubt and the offer of a position on Middlesbrough’s coaching staff could appeal.

The 38-year-old Argentinian was a team-mate of both Karanka and Boro goalkeeping coach Leo Percovich in Colorado in the 2006 season, and the trio became close friends during their time together in the United States.

Percovich accompanied Karanka during the interview process that led to him being installed as Boro head coach, and enjoys a wider remit than his official job title of goalkeeping coach would suggest.

He is expected to take over touchline duties in Hignett’s absence if Karanka receives a touchline ban following the Football Association’s decision to charge him with improper conduct on Tuesday, and is likely to be involved in discussions over any potential addition to the backroom staff.

Mastroeni is unlikely to be offered a position imminently, but the situation could quickly change if the Colorado Rapids were to make a sluggish start to the new MLS season.

“Pablo is hoping to spend some time with Aitor, another former player that has moved on to coaching, to share ideas,” confirmed Colorado Rapids vice-president of soccer operations and technical director Paul Bravo. “This, therefore, represents a great opportunity for our head coach to go and further his education.”

With Percovich and fitness coach Carlos Cachada to lean on, Karanka is in no rush to appoint a permanent replacement for Hignett, who stepped down from his position as number two on Tuesday morning.

There have been suggestions of a confrontation between the former striker and Karanka in the wake of Saturday’s controversial 1-1 draw with Blackburn Rovers, although it is understood the pair’s relationship had begun to deteriorate before the weekend.

There was more bad news in what has been a difficult week for Middlesbrough yesterday, with Ryan Fredericks taking to Twitter to confirm he has been ruled out with injury until the New Year.

Fredericks limped out of Saturday’s game after damaging his thigh, and scans have revealed significant damage that will force the full-back to miss the whole of the festive programme.

“Bad news with the injury,” tweeted Fredericks. “Hoping to be back for the start of January and back up at the top of the table thanks for all the messages.”

Having replaced Fredericks in the Blackburn game, Emilio Nsue will step into the right-back breach for the next few weeks, with Damia Abella also unavailable.

Boro are also sweating over the availability of Dimi Konstantopoulos and Daniel Ayala ahead of Saturday’s trip to Millwall, with the pair having picked up knocks in the controversial closing stages of Saturday’s game.