Matic has recently been linked with a summer move to Italian side Juventus, although the 27-year-old still has three years left on his current deal at Stamford Bridge.
"I have my reasons," he said after the game at the Stadium of Light.
"Everything can change in a couple of months."
Matic also suggested that Chelsea captain John Terry, who will be suspended for the club's final two games of the season after being sent off late on against Sunderland, will not stay on past this summer.
"We know what he has done for this club and what he has won," Matic said.
"All of us in the team wish him all the best for the future. Of course this is not a good way to finish in a club, but we don't forget what he won and what he has already done."