Brazilian Nasr has just completed his second season with Sauber and picked up two points in 2016 to help them finish ahead of Manor in the Constructors’ Championship.
However, Banco do Brasil announced ahead of the Abu Dhabi GP that they would no longer sponsor the team due to branch closures in Brazil.
The withdrawal of the sponsor has left Nasr’s future up in the air and Kaltenborn is eager to resolve the situation as quickly as possible.
Kaltenborn said: “His major sponsor took a position which the publicly announced and we obviously accept that.
“It plays into the assessment of course, which we are making still. We still have not come to a decision but we want to resolve it as soon as possible.
“However, it takes more than our side to get that done, so we’re on it and I still hope that we can quite quickly resolve it.”
Tottenham have joined the race to PSV Eindhoven winger Steven Bergwijn, who is on the wanted list of a number of clubs.
West Ham striker Marko Arnautovic has dismissed reports linking him with a move to Manchester United.