Brighton have signed striker Sam Baldock from Bristol City on a four-year deal for an undisclosed fee.
Tottenham have signed Sevilla defender Federico Fazio on a four-year contract.
Reports have suggested Wolfsburg are lining up a move to sign the 28-year-old in the summer to bolster their defence.
Wolfsburg general manager, Klaus Allofs, is a big fan of Mertesacker having worked with him during their time together at Werder Bremen.
Mertesacker's future at Arsenal has been the subject of conjecture after coming in for criticism for some of his performances for Arsene Wenger's side.
However, Mertesacker insists he is happy at Arsenal and has no plans to return to his homeland.
"No, I don't consider a return to Germany. I am under contract with Arsenal and I am planning to stay on at Arsenal for more years from now," Mertesacker told Sport-BILD.