Tony Pulis says that new arrival Jordan Hugill will take a few weeks to get up to speed at Boro, and ruled him out of contention for Saturday's home match against Birmingham City (3pm).
Striker Hugill arrived on a season-long loan from West Ham United on Wednesday.
And though the Boro-born 26-year-old is itching to get going, the Boro boss says he'll be patient with his new man.
"Jordan's been injured, and hasn't had a full pre-season," Pulis said.
"It will take us a few weeks to get him properly fit and ready. I think it will be the international break before we'll see him."
Meanwhile, there's better news for Jonny Howson, who was withdrawn in the second half of Tuesday's victory over Sheffield United.
"Jonny got a kick rather than a strain or a pull so we're expecting him to be fit," Pulis said "I think out of the two games, he's been our outstanding player.
"I thought he was exceptional at Millwall when things weren't going so well and again on Tuesday night, his work in midfield getting forward and back."