Arsenal must "improve massively" if they are to continue winning games, says manager Mikel Arteta after the Gunners were held by Sporting CP in an entertaining Europa League last-16 first leg.
France defender William Saliba put the Premier League leaders ahead with a towering header before Sporting took advantage of poor defending to score through Goncalo Inacio and Paulinho.
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.
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."