BMW to announce 2009 drivers in August
It is believed that struggling Nick Heidfeld has a contract for next year, while the status of his teammate Robert Kubica is less clear.
Theissen was asked by Spain's Diario Sport about rumors linking Fernando Alonso to the team for 2009.
"I will not talk about this or any other matter relating to contracts. We have an agreement with our drivers that prevent us from talking about it," he explained.
The German did, however, acknowledge that Alonso, 26, is one of the F1 drivers he most highly rates.
"Raikkonen, Hamilton, Alonso and Kubica," he said, when asked to list F1's best drivers, "and Massa close to them."
On the same topic, Theissen issued a clear "no comment" to a correspondent of the Spanish newspaper AS.
"We have a very clear policy to not say anything until August. We will make an announcement then."
But he did say of Alonso's season with Renault this year: "Obviously it is not good for a champion to have a bad season."