Middlesbrough have confirmed that full back Julio Arca has broken his foot.
The Argentine picked up the injury during Boro's opening day 3-2 defeat at Reading.
He is now expected to be sidelined for around three weeks, which is a huge blow for manager Gareth Southgate.
Boro are already short of defensive cover, but now they have further problems to worry about ahead of Wednesday's daunting clash with champions Chelsea.
Southgate's options include calling up England Under-21 ace Andrew Taylor, switching Emanuel Pogatetz back to left back or indeed shifting Stuart Parnaby from right back.