An own goal by the hosts' Japanese midfielder Hidemasa Morita ensured Arsenal will start on level terms when the teams meet in the return leg at Emirates Stadium next Thursday (20:00 GMT).

However, Arteta was unimpressed his side had conceded two goals for the second successive game.

"It's true that it's something that we must improve massively if we want to keep winning games," said the Spaniard.

"When you concede two poor goals like we did away from home in Europe it's very difficult to get a positive result.

"We gave too many simple balls away. We need to defend our box much better."

In an absorbing game in the Portuguese capital, Arsenal's first-half lead lasted just 12 minutes before Inacio nodded home the equaliser after hesitancy from keeper Matt Turner.

Paulinho fired Sporting ahead from close range only for Arsenal to equalise through a wicked deflection off Morita.

Both teams created numerous chances in a free-flowing encounter.

Sporting's former Tottenham winger Marcus Edwards was denied by Turner when the score was 1-1, while Paulinho wasted a great opportunity to make it 3-1.

Arsenal had a chance to take a lead back to London but Fabio Vieira's header was kept out by Antonio Adan.

Arteta faces balancing act in Arsenal's trophy hunt

Arsenal are chasing a first Premier League title since 2003-04 but Arteta clearly sees the Europa League as something worth winning rather than a distraction to the main prize.

Despite making six changes, he fielded several key players in Portugal including Gabriel Martinelli - Arsenal's leading scorer in the Premier League - and Bukayo Saka before Sunday's London derby at Fulham (14:00).

It is all to play for in seven days' time in the return leg against Sporting, but Arteta's side will have to improve defensively if they are to advance to the quarter-finals against opponents who started the season in the Champions League.

Poland defender Jakub Kiwior made his first Arsenal appearance since arriving in January from Serie A side Spezia for £17.6m while Turner produced a mixed performance after replacing first-choice keeper Aaron Ramsdale.

The Gunners were sloppy at times and the two goals they conceded were poor by their recent standards but, just as they did against Bournemouth at the weekend, they showed character after falling behind and continue to look a threat going forward.

Martinelli was denied after trying to clip the ball over the keeper at the start of the second half before the Brazil forward looked certain to score after a superb solo run only to be denied by a well-timed challenge by Jeremiah St Juste.

The games are starting to come thick and fast for the Gunners and Arteta faces a fine balancing act as his side chase domestic and European honours.

"In this competition if you want to go through you have to go through difficult moments," the Arsenal boss said. "We're still alive and hopefully we'll play better at the Emirates."

Arsenal reached the last 16 by topping their group with five wins from six matches