VfB Stuttgart forward Deniz Undav is doubtful for the Bundesliga match against Eintracht Frankfurt on Sunday. Undav was subbed off during the 2-0 defeat to Atalanta in the Champions League on Wednesday with a muscular issue. Stuttgart said on Thursday that he suffered a strain on his left thigh. His participation in the match against Frankfurt is “questionable, but not ruled out.” Undav is expected, however, to join the Germany national team for the Nations League matches against Bosnia-Herzegovina on November 16 and in Hungary three days later. He was named to the squad by coach Julian Nagels…