Danilo Pantic
Partizan Belgrade midfielder Danilo Pantic (R) has been confirmed as Chelsea's fourth summer signingGetty

Chelsea have confirmed the signing of Serbian midfielder Danilo Pantic from Partizan Belgrade on a long-term deal.

"Chelsea Football Club is delighted to announce the signing of Danilo Pantic from Partizan Belgrade, with the player immediately joining Vitesse Arnhem for the forthcoming campaign," a statement on the Blues' official site read.

The Serbian youth international, who can operate either as a central midfielder or on the left of midfield played a key role in helping his country's U19 team reach the semi-finals of the European U19 Championships in 2014.

Pantic, who was immediately loaned to Vitesse in the Eredivisie, has expressed his delight at joining the Premier League champions and is hoping to impress while on loan with the Dutch club.

"I am very happy to sign for Chelsea, the champions of the English Premier League, and I hope I can show my value at Vitesse in the coming season. I am honoured at the faith both clubs have shown in me," the Serbian U19 international said, as quoted on Chelsea's official site.

The former Partizan midfielder had confirmed the deal in early July, when he revealed that he had agreed a contract with the Blues in June ahead of his loan move to Vitesse.

Pantic becomes Chelsea's fourth summer signing following the arrivals of Asmir Begovic, Radamel Falcao and Brazilian youngster Nathan.

Meanwhile, Jose Mourinho has expressed his disappointment following Chelsea's 4-2 loss at the hands of MLS club New York Red Bulls on 22 July.

The Portuguese manager blamed his team's poor defence, and believes that they made it too easy for their opponents to score goals, and this despite the Blues fielding a strong XI in the second half.

"The team in the second half they could not defend. We cannot concede four goals in 45 minutes against a top team, and we cannot concede four goals in 45 minutes against a team with the young guys from Red Bulls," Mourinho said, as quoted on Chelsea's official site.

"It was too easy. Every chance they created was a goal and obviously our team in the second half was a very strong team – Terry, Zouma, Azpilicueta, Ramires, Matic. It was a very strong team so obviously I was disappointed," the Portuguese manager added.