CSKA Sofia signed Algeria goalkeeper Rais Mbolhi on loan from city rivals Slavia on Tuesday.
"It's a big challenge to play in the Europa League," Mbolhi told reporters.
CSKA, Bulgarian champions 31 times, have been drawn alongside Porto, Besiktas and Rapid Vienna in Group L. The French-born Mbolhi, 24, played at the 2010 World Cup.
