Lewandowski scored the second goal in Poland's win against Lithuania
Striker Robert Lewandowski has a hamstring injury and could miss Barcelona's game against Real Madrid later this month.
The 37-year-old, who scored for Poland in a 2-0 World Cup qualifying win against Lithuania on Sunday, will not feature in his club's La Liga game against Girona this weekend.
Barcelona then face Olympiakos in the Champions League next Tuesday before taking on Real Madrid in El Clasico at the Bernabeu on 26 October.
Barcelona have not indicated how long Lewandowski is expected to be missing for, but Spanish media have suggested
