Borussia Dortmund are set to offer Bayer Leverkusen defender Omer Toprak €20 million according to Turkish newspaper Milliyet.
The report claims that Dortmund are considering bringing in Toprak to replace Matt Hummels who joined Bayern Munich.
Topeka still has another two-years left on his current deal but a clause in his contract means that he will have a €12 million release clause next season so Bayer may be tempted to cash in.
The Turkish international defender joined Bayer in 2011 and has a wealth of Bundesliga, Champions League and international experience.
Dortmund could face competition from United who have been keeping close tabs on Torpak according to the Express.
German media outlet Kicker also reported that United sent scouts to watch Toprak over the course of the season.
United struggled defensively last season and bolstering their options at the back will be priority for the manager who replaces Louis van Gaal.
Toprak was left out of the preliminary Euro 2016 squad after failing to patch up his differences with Gokhan Tore who was involved in a gun-incident.
The 26-year-old defender has since revealed that he would consider returning for the European Championships after making up with Tore and is expected to be recalled.