CSKA had last season some problems with left wing. At pre-season, there was bought Yuri Zhirkov from Second Division club Spartak Tambov and Osmar Ferreira. I think that the idea was that Osmar had to play in first team, but: Zhirkov was bought earlier and spend all the pre-season training with the team, and Ferreira joined the team only at last (fourth) camp at Holland. So Zhirkov had been in better form and had the chance and used this chance. He played (and still play) very well.
So Osmar was used sometimes as left wingback, although he has played at this position at national U'21 team, effects in CSKA was not very good. Also Daniel Carvalho was in competition at left wing.
After the change of coach, Ferreira have not been used as wingback and he is the first reserve as left winger, 'cause Carvalho is currently injured. He played a week ago in Russian Cup match, but have not scored having very good opportunity. Maybe it is question of self confidence. But he is young and I think he'll be good player for the team.
About your second question:
Cavenaghi have not been submited to Spartak's official squad list of Russian Premier League and have not played single match. AFAIK
, he didn't arrive to Moscow yet (he was in Moscow when he was negotiating his contract, but returned to Argentina and should be in Moscow this week).