They do not seem inclined to stop there, and have also been linked with Leicester back Ben Chilwell and Bayer Leverkusen, the winger Kai Havertz.
But speaking to StarSport, Merson, said to Sancho – who has scored 17 goals and created 16 assists in the Bundesliga this season, is the player Chelsea should concentrate on trying to sign.
“I don’t think that Chelsea’s spending stops (with Ziyech and Werner),” Merson said.
“It is obvious that they still want to Jadon Sancho, and if they can’t get him they will probably try to Kai Havertz.
“One of them is going to cost nearly £ 100m. But this kind of transfer pays for itself. Chelsea could get a good five years of Sancho, and still get a great resell.
“You have all the chances to recover your money with a player like Sancho. And if Abramovich starts to come to matches again, they want to be entertained. It not care to pay £100m for a Sancho, if it allows them to play good football.
Mirror Football Top Stories
“The signature of Werner is a big statement. But the signature Sancho would be an even bigger one. ”
Much will depend on Chelsea to qualify for the Champions League with the Blues currently sitting in fourth place, just three points above United.
They travel to Aston Villa on Sunday ahead of two tricky-looking games against Manchester City and Leicester were followed by a London derby against West Ham.