Barcelona’s teenage sensation Lamine Yamal missed training on Thursday, sparking concerns ahead of Sunday’s La Liga clash with Sevilla. The 18-year-old, who rescued a 1-1 draw for Barca against Newcastle in the first leg of their Champions League round of 16 tie on Tuesday night, is said to be struggling with illness.Barcelona returned to the grass on Thursday at the Ciutat Esportiva Joan Gamper, but there was a high-profile absentee from the group session led by Hansi Flick. After a period of rest following their Champions League travels, the Catalan giants were back in training action at the Camp Tito Vilanova, though Yamal was nowhere to be seen.The La Masia graduate did not participate in the workout alongside his team-mates, with Barca revealing he was dealing with "general discomfort" in an official statement. Diario AShave reported that Yamal has been laid low with illness, though he is expected to return to training on Friday.Yamal's absence is particularly notable given his starring role in the first-leg encounter against Newcastle at St. James' Park. He displayed nerves of steel to convert a penalty deep into stoppage time after Joe Willock had committed a foul on Dani Olmo inside the area, securing a valuable 1-1 draw on English soil.That late strike has changed the complexion of the tie, giving Barcelona a psychological edge as they head back to the Catalan capital. The squad returned from Newcastle with an improved outlook thanks to Yamal’s contributions, knowing they can seal their place in the quarter-finals when the Premier League side visits the Spotify Camp Nou next Wednesday. However, keeping their talisman fit and healthy is now the top priority for Hansi Flick and his medical staff.Yamal has accumulated 3,102 minutes of action this season, the second-highest total in the entire squad behind only Eric Garcia, who leads with 3,208 minutes. His durability has been key to Barcelona’s consistency across multiple competitions, making this latest bout of illness a significant talking point.His statistical output is equally staggering, leading the club charts for direct goal involvements with 20 goals and 15 assists. His scoring tally includes 14 strikes in La Liga, four in the Champions League, and two in the Copa del Rey. With 10 league assists and three more in Europe, Yamal has been the primary engine driving Barcelona's offensive output, and any potential absence from the matchday squad would leave a massive void in Flick's attacking blueprint.Add GOAL.com as a preferred source on Google to see more of our reportingThe club remains optimistic that Yamal will be available for selection this weekend. If the youngster recovers from his illness as expected and rejoins the squad for Friday's session, he should be in line to maintain his starting spot against Sevilla.Flick will be keeping a close eye on the player's recovery over the next 24 hours. The German manager is well aware that he cannot afford to lose a player who has provided such a consistent spark in the final third. With the return leg against Newcastle looming large after the Sevilla game, the management of Yamal's workload and health will be critical.