Chelsea risk losing Mateo Kovacic at the end of the season.
The midfielder is on-loan at Chelsea from Real Madrid with no permanent option.
The Daily Mail says Kovacic could join Zenit St Petersburg this summer.
Kovacic's agent held talks with Zenit this week over a possible move.
Kovacic has impressed at Chelsea this season, with Maurizio Sarri publicly revealing he hopes to keep the Croatia international at Stamford Bridge.