But Wehrlein has branded reports of a done deal as "fictitious".
Sauber team boss Monisha Kaltenborn has also revealed that talks with Nasr are still taking place, with him still retaining some Banco do Brasil backing, albeit in a much reduced form.
"We have our options, we are looking at them and we know Felipe very well. We're just going to continue our assessment and when we're ready we'll announce," she said.
Mercedes boss Toto Wolff said Mercedes is still deciding the 22-year-old's future.
"We are in discussion with Monisha and in discussion with (Manor owner) Stephen (Fitzpatrick) and nothing is decided yet," said the Mercedes team boss.
Bahrain International Circuit - Winter testing