Dortmund splashes out on Mainz defender Diallo

Abdou Diallo has become Borussia Dortmund's second-most expensive signing after his arrival from Mainz on a five-year contract was confirmed.

Dortmund is understood to have shelled out €28million to snare the centre-back, eclipsing its outlay for Henrikh Mkhitaryan but falling short of the €30m spent on Andre Schurrle in 2016.

Diallo impressed in his solitary season for Mainz, making 30 appearances in all competitions following his arrival from Monaco for a reported fee of just €5m.

"After getting to know the Bundesliga at Mainz, I am looking forward to the challenge of being able to prove myself at a club as big as Borussia Dortmund," the 22-year-old said.

"Together with my team-mates, I want to justify the trust placed in me and do my part to ensure that BVB achieves its goals in all competitions.

"Now I cannot wait to start preparing for the new season under Lucien Favre."