Mercedes team chairman Niki Lauda has warned that it could take until February to decide who will replace Nico Rosberg.
Following the German's shock retirement after he was crowned world champion last month, Mercedes said that they would make no decision until after the team returns from their Christmas break on January 3.
But now Lauda has hinted the wait could be even longer.
"It could take until the end of January before we know what path we are going to take," he said.
"We are not ready yet. There are quite complicated negotiations," he added.
Meanwhile, it has been said that Lewis Hamilton vetoed the idea of Wehrlein stepping in, fearing a repeat of the situation he faces in his rookie season at McLaren when he partnered double world champion Fernando Alonso.
Bahrain International Circuit - Winter testing