Manchester City forward Raheem Sterling has been ruled out of England’s upcoming matches against Spain and Switzerland due to a back problem.The 23-year-old withdrew from the squad on Monday as the other 22 players assembled for a training camp at St George’s Park.Sterling’s absence comes as a blow to Gareth Southgate despite questions being raised over his international record. Article continues below Editors’ Picks Man Utd ready to spend big on Sancho and Haaland in January Who is Marcus Thuram? Lilian’s son who is top of the Bundesliga with Borussia Monchengladbach Brazil, beware! Messi and Argentina out for revenge after Copa controversy Best player in MLS? Zlatan wasn’t even the best player in LA! He has netted just twice in 44 appearances and failed to get on the scoresheet as England finished fourth at the World Cup in Russia.However, the attacker remains a regular under Southgate and has started the season in fine form, scoring twice in four Premier League matches.His second came in City’s weekend win over Newcastle United, in which he played a full 90 minutes.”Raheem Sterling has withdrawn from the squad due to a problem with his back, with no immediate replacement planned,” read a Football Association statement.Southgate is already thin on options in the front third following Jamie Vardy’s decision to step back from international duty .England open their Nations League campaign against Spain at Wembley on Saturday, with a friendly against Switzerland at King Power Stadium to follow three days later.