Middlesbrough boss Gareth Southgate says £6m centre-back Robert Huth is not ready for first-team action.
An ankle operation delayed Huth's move from Chelsea
Huth, 22, has recovered from an ankle injury and followed up a reserve outing by playing the full game in the defeat by Notts County in the Carling Cup.
"Robert is only really at the start of his pre-season," said Southgate, who signed Huth from Chelsea in the summer.
"But he still needs a couple more weeks of training and matches to be up to speed for the first team."
Huth is set to play for the reserves against Manchester United on Wednesday as he builds up his fitness.
"He has had 60 minutes in the reserves and I did not really want him to play the full 90 against Notts County," said Southgate.
"He managed to get through, but he needs more work fitness-wise.
"Normally those matches would be behind closed doors in pre-season against a non-league side or a lower division team in a friendly.
"But I threw him into a competitive game and he will be far better for that."