However, Wenger is hopeful they will agree to extend their Emirates Stadium careers.
"We are speaking with Tomas and William, and I am optimistic to find a solution for both of them," he said in The People.
Wenger is also eager for Vela to commit his future to the club as he has a lot of faith in the 20-year-old Mexican.
The Gunners boss has likened Vela to former Liverpool forward Robbie Fowler and praised his composure in front of goal.
"We've had no offers for Carlos and we are extending his contract at the moment," said Wenger.
"The problem we have is that we have some very good young players, but the players who are in front of them are also young.
"But Carlos was the reason I didn't replace Emmanuel Adebayor in the summer.
"He's that good. He's like Robbie Fowler, in that he needs very little time to make a decision in the box, he is very relaxed when he finishes."