Arsene Wenger admits he is baffled by another hamstring injury that is likely to rule out Aaron Ramsey for at least four weeks.
The Welshman lasted only nine minutes of Tuesday night's 2-1 win over Leicester before being forced off the pitch; he has only recently returned from a six-week lay-off over Christmas with the same injury.
Reports now suggest that Ramsey will miss another month.
"It looks like it (a recurrence of a hamstring injury). I don't know how bad it is yet. Just visually, it didn't look good - when a guy stops straight away and sits down, that's not good news," said Wenger on Tuesday night.
"There's a recurrence now of a few muscular injuries and it's difficult - we haven't found out why."
The good news for Arsenal fans is that Alexis Sanchez is unlikely to miss a Premier League game with the bang he suffered to his knee, though he could be rested for Sunday's FA cup clash with Middlesbrough.