Henrikh Mkhitaryan and Marcel Schmelzer
Marcel Schmelzer knows that replacing Henrikh Mkhitaryan will be a huge challenge for Dortmund PATRIK STOLLARZ/AFP/Getty Images

Borussia Dortmund stalwart Marcel Schmelzer has expressed his surprise at former teammate Henrikh Mkhitaryan's decision to depart for Manchester United.

The highly-rated Armenian playmaker was confirmed as the third new signing of Jose Mourinho's early reign at Old Trafford on Wednesday afternoon (6 July), following on from the respective additions of Villarreal centre-back Eric Bailly and high-profile free agent Zlatan Ibrahimovic.

BVB announced over the weekend that they had reluctantly accepted a "tremendous" offer believed to be in the region of £26m ($33.5m) for Mkhitaryan, whose previous contract at Westfalenstadion was due to expire in June 2017. Such confirmation came as another hefty blow to the Bundesliga runners-up, who have already lost the services of two influential players in Mats Hummels and Ilkay Gundogan this summer.

Recovering from the loss of an attacking talent who registered 23 goals and 32 assists across all competitions in 2015/16 will certainly not be easy and long-serving left-back Schmelzer is only too aware of the difficulties that lie ahead as Dortmund desperately seek to keep pace with reigning champions Bayern Munich, who have a new manager at the helm in Carlo Ancelotti.

"I was surprised that Micki decided to make the move after all," he was quoted as saying by The Mirror at a recent press conference. "Many players after the season talked to him about his plans. In the end, all you can do is to accept the decision.

"It's a major upheaval when your captain leaves and also a player like 'Micki', who's had a hand in 55 goals last season. The key now will be to offset it as a team. We have signed a lot of talented players, who will have to grow into their role. It will be difficult in any case because you can't replace Mats and Micki like-for-like."

Thomas Tuchel's Dortmund, who have finished second behind Bayern in three of the last four seasons, have been active in the transfer market themselves over recent weeks and beat a host of other top suitors to the signing of exciting 19-year-old France forward Ousmane Dembele in May. Midfielder Sebastian Rode has also joined from Bayern, while Portuguese international Raphael Guerreiro arrives from FC Lorient. Barcelona's Marc Bartra and Osasuna midfielder Mikel Merino have also been recruited.