Newcastle boss Eddie Howe says defender Dan Burn's expected long-term absence with a back problem is "a huge blow".
The left-back, 31, was replaced at half-time during Saturday's 1-0 win over Arsenal in the Premier League.
Howe says fellow left-back Matt Targett is also unavailable for "around three months" with a hamstring injury suffered in the Carabao Cup win at Manchester United on 1 November.
"Dan Burn will be out for some time," Howe said on Monday.
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"It's another long-term problem.