Toro Rosso Formula 1 boss Franz Tost claims James Key still has a "valid contract" with the team despite McLaren announcing he would be joining as its new technical director.

McLaren announced on Thursday morning that Key would be arriving at the team as its new technical director, but gave no details on a start date. Key replaces Tim Goss, who departed McLaren back in April, with engineering director Matt Morris' resignation also being confirmed on Thursday.

Hungarian GP - Best Moments

In the wake of the announcement, Toro Rosso posted a tweet quoting Tost, who said Key was still under contract with the team.

"James Key has a long-term valid contract with the team. The contents of the contract are confidential, therefore we won’t comment on any of the details," the tweet read.

Key is not present in Budapest for the Hungarian Grand Prix, but was already planned to work on the race remotely, having also not attended last weekend's event at Hockenheim.

Drivers Pierre Gasly and Brendon Hartley also remained coy when asked about Key's reported departure on Thursday afternoon.

"On my side, I don't really want to comment too much about it, because the situation is still not really clear," Gasly said.

"I saw, like everyone, what McLaren said this morning, but I saw, like everyone, what Toro Rosso said afterwards. So it's not so clear.

"Of course he is really important inside the team as technical director. He brings a lot of performance, and it would be sad to lose a key element within the team. It would be a shame to lose him."

Hartley added: "He's been here for a long time, before I was here this year. James is good to work with. It's a big team of people. It never falls just on one person's shoulder, obviously. He's an important part of the team.

"But in terms of answering comments about if he's leaving, if he's staying, I don't really have anything to say and I don't really want to be in the headlines making comments on it."