The Brazilian midfielder could make his debut against Southampton on Saturday amid talk of United returning to the market in an £84m deal for Ajax forward Antony.
“We need players but we need the right players,” Ten Hag told reporters on Friday.
“The whole transfer window, we are happy with what we did until now, but the bar has to be high.”
“Casemiro is fit,” he added. “He did all the training sessions. He trained first individually and the last days he trained with the team.
“Martial came out with a problem on his Achilles, out of the game, so we have to wait.
“I cannot tell a prognosis, how long it takes. I hope he will be available for the next game [at Leicester on Thursday].”