Bundesliga strugglers Borussia Dortmund have agreed to sign Slovenia international Kevin Kampl in January.
Cardiff have agreed to sell Norwegian midfielder Mats Daehli to Freiburg in January.
The 29-year-old France international, signed from Toulouse in 2009, played 25 games for Los Che last season, scoring twice.
Mathieu, while participating in the new season's kit launch, told valenciacf.com: "I am delighted to renew with Valencia, in this great club.
"I feel great and very happy to stay several more years in Valencia."