Goalkeeper Cillessen – who joined the Spanish club in August to replace the departed Claudio Bravo – hurt his knee while training with his Netherlands team-mates on Saturday.
A scan on Monday revealed the 27-year-old had sprained ligaments in his right ankle, ruling him out for approximately three weeks.
Cillessen’s solitary appearance since arriving from Ajax came in the shock 2-1 loss against Alaves on September 10.
Roberto, however, has been heavily involved during the 2016-17 season so far, making eight appearances in all competitions.
The Spain international missed his nation’s 2-0 win over Albania on Sunday after picking up an injury in training ahead of the 2018 World Cup qualifier.
A statement on Barcelona’s official website confirmed Roberto suffered a strain in his right abductor, with an update on his availability to follow “in the coming days”.
Barcelona host Deportivo La Coruna on Saturday before welcoming former coach Pep Guardiola’s Manchester City to the Camp Nou next Wednesday in Champions League action.