Arsenal manager Mikel Arteta has urged teenage left-back Myles Lewis-Skelly to recognise the "thin line" when it comes to discipline on the pitch following a series of bookings and red cards.
The 18-year-old defender has faced disciplinary issues since January, receiving two yellow cards and two red cards in that period, prompting Arteta to highlight the importance of learning from his mistakes.
During Arsenal's 7-1 Champions League victory over PSV on Tuesday, Lewis-Skelly was substituted after a yellow card and a rash challenge on Richard Ledezma.
Arteta, acknowledging the need for improvement, said: "A lesson to learn for him for sure. We will support and help him. The line is really thin in sport and he needs to understand that."
The Arsenal coach further emphasised that the player's intelligence and high self-demands would serve him well in his development, although he must refine his approach to avoid unnecessary risks.
Since making his senior debut in September during Arsenal's 2-2 draw with Manchester City, the left-back has experienced a rollercoaster start to his career.
Looking ahead to Sunday's Premier League clash with Manchester United at Old Trafford, the Spanish boss shared his advice for Lewis-Skelly, stressing the importance of evaluating the situation before going into tackles.
"You need to dominate the space you are defending," Arteta explained, urging his player to weigh up the risks and follow defensive principles to avoid costly mistakes at this level.