Back in January, Arsenal were trailing at home against Manchester United when the ball went out for a corner and Nicolas Jover did as he always does.

Back in January, Arsenal were trailing at home against Manchester United when the ball went out for a corner and Nicolas Jover did as he always does.

Mikel Arteta's set-piece coach raced to the edge of the technical area and began to pull the strings.  Soon, though, the Frenchman was wagging his finger: Arsenal had gone off-script and played it short.

 His frustration didn't last - a few passes later, Granit Xhaka clipped a cross on to the head of Eddie Nketiah and Jover joined in the wild celebrations.

 In Lisbon last night, Arsenal abandoned best-laid plans once more.  This time, there was nothing to soothe Jover's ire.

 This time, from a Sporting corner, Gabriel Martinelli allowed Goncalo Inacio a run on goal, goalkeeper Matt Turner stayed put and debutant Jakub Kiwior left the ball for Inacio to head home an equaliser.

It was really poor;  it has become a theme.  Arsenal have now conceded four goals from corners since the World Cup - twice as many as they shipped in 21 matches before the mid-season break.

 Penalties aside, they have been undone from set-pieces in five of their past 10 matches.  Before Christmas, it happened just twice.

 'It's true that it's something we must improve dramatically in the next few games if we want to keep winning,' Arteta said after this Europa League draw.  We are conceding too many simple goals.

 The manager was at a loss to explain the series of errors that allowed Sporting back in the game: 'I don't know what it was.  It happened in a second split but for sure in that space somebody cannot have a free header.

Arteta did, though, did offer some mitigation for Arsenal's recent struggles: 'Sometimes the opponents are really good at what they do.  When they get the delivery in the right space it’s just half a centimeter sometimes whether you get that header out of the box or it goes in.’

 It's true - football is a game flush with randomness and fine margins.  It's also true that Sunday's opponents Fulham are very dangerous from dead-balls: only Tottenham (12) have scored more goals from set-pieces this season than Marco Silva's side (11).

 Aleksandar Mitrovic (four) and Bobby De Cordova-Reid (three) sit third and joint fourth, respectively, for headed goals in this season's Premier League.  No other team has two players with more than a couple.

 So another test lies right around the corner.  Time and again recently, Arteta's side have dug themselves in and out of holes.  They cannot keep making life so difficult.

Particularly at this point in the season, when games grow more tense, every error is amplified, and dead balls are even more pivotal.

 The impact of Jover, who worked with Arteta at Manchester City, cannot be underestimated: in 2020/21, the season before he arrived, Arsenal scored six goals from set pieces – fewer than all but two teams.  Last season, their tally of 16 put them third.  This year they sit joint-second on the 11th.

 At the other end, however, the upward curve has been rather less smooth.  Across the last four Premier League seasons, Arsenal's defensive record from set pieces reads: 15 goals conceded (tied 15th), five (top), eight (sixth), five (tied sixth).

 This latest mishap might have been avoided had Gabriel and Aaron Ramsdale play.  Instead, Arsenal lacked cohesion across the pitch after Arteta shuffled his pack.  Their preparations had been hampered by illness and injury.

Arsenal initially planned to stay overnight and train in Lisbon on Friday morning, only to change tack and fly home after the game.

 Hence why plans to bring striker Gabriel Jesus were abandoned.

 Captain Martin Odegaard, one of several players to have been unwell, hopes to recover in time for the trip to Craven Cottage.

 But Arsenal's busy schedule doesn't leave much time to remedy more lingering problems.