Madrid, Nov 24 : Concerns are growing about the fitness of FC Barcelona goalkeeper Marc-Andre ter Stegen as he was absent from training, just 48 hours ahead of Barca's La Liga match against Rayo Vallecano. Ter Stegen returned to Barcelona from the German national team training camp on November 19 with a back problem that prevented him from participating in the matches against Turkey and Austria, reports Xinhua. "He has a lot of pain in his back. He will return to Barcelona," explained Germany coach Julian Nagelsmann, who suggested the problem wasn't serious. "I hope he will soon be available to play for his team," he added. However, five days after returning to Barcelona, ter Stegen has yet to participate in training. Barca hopes to have him ready for next Tuesday's Champions League tie against Porto. Should ter Stegen not recover in time, it opens the door for 24-year-old Inaki Pena, who has yet to play in a competitive match this season. Pena's first team experience at Barca is limited to two appearances in La Liga last season, one in the Champions League, and two games in the Copa del Rey. Barca is also without Gavi for the rest of the season after he suffered a knee injury while playing for Spain. Sergi Roberto is also sidelined with a calf injury. /IANS