MIDDLESBROUGH have completed the capture of Viktor Fischer, but the Teessiders have been warned off making a fresh approach for long-term transfer target Michail Antonio.

Fischer, who has become Boro’s first signing since winning promotion to the Premier League, was at Rockliffe Park yesterday undergoing a medical and putting the finishing touches to his €5m move from Dutch side Ajax.

Having passed his medical examination, the Danish winger has signed a three-year deal, with an option for a fourth year on his contract, although his transfer cannot be officially ratified until the international transfer window opens on June 9.

Aitor Karanka is not currently working in the North-East, but the Boro head coach has been regularly updated on developments and is understood to regard Fischer’s capture as a significant coup.

The 21-year-old, who is a right-footed winger who tends to play on the left-hand side, was considered one of the most exciting youngsters in Europe when he broke into Ajax’s first team in 2013 and helped the club claim the Eredivisie title.

At that time, he was rated in the same bracket as fellow Danish national Christian Eriksen, and his emergence led to interest from Bayern Munich, Manchester United and Manchester City, all of whom approached Ajax to inquire about his services.

Ajax boss Frank de Boer tied him down by offering him a contract to 2017, but his career stalled significantly when he suffered a hamstring injury in February 2014. The tear initially looked fairly routine, but complications meant he was sidelined for more than a year and did not return to the first team until April 2015.

The length of that injury meant Boro’s medical staff were instructed to oversee a particularly rigorous medical, with the Teessiders determined to take no chances as they look to ensure they have a strong enough squad to survive in the top-flight next season.

Fischer found himself on the fringe of the first-team picture at Ajax in the second half of last term, with his final appearance coming in the 1-1 draw with De Graafschap on the final day of the campaign that resulted in the title going to PSV Eindhoven.

That led to de Boer’s departure from the Amsterdam ArenA, and Boro have taken advantage of the state of flux to conclude a swift deal for the midfielder.

Fischer is currently on international duty with Denmark, but with the Danes having failed to qualify for this summer’s European Championships, he was given permission to leave his national side’s training camp in order to travel to England.

He was accompanied by his agent, former Denmark international Soren Lerby, but will return to his homeland ahead of the Danes’ trip to Japan for the Kirin Cup.

Fischer’s arrival could have implications for Stewart Downing and Christian Stuani, who played on the left-hand side on a number of occasions last season, and should see Albert Adomah reverting to the right.

Karanka’s search for new wide players saw him once again linked with Antonio earlier this week, with Boro having tried unsuccessfully to sign the winger before he moved to West Ham from Nottingham Forest.

Boro lodged a number of bids with the Forest hierarchy last August, only for Antonio to complete a £7m move to Upton Park at the start of September.

The winger has proved a success with the Hammers, and West Ham co-chairman David Gold produced a withering response to suggestions that Boro were ready to make a renewed attempt to sign their former target.

Writing on Twitter, Gold reproduced a tweet from the London Evening Standard flagging up Boro’s interest, with the reply: “Dream on”.