Cerra sustained a low-grade hamstring strain during last week's upset of AFL ladder-leaders Collingwood and is set to miss up to three matches.
The injury came a week after Cerra sat out the round-19 thumping of West Coast because of "hamstring awareness".
Fellow midfield gun Walsh strained a hamstring during that win over the Eagles and won't be back until at least round 23.
"We'll be pretty diligent with where we think he's at and the timeline's there," Voss told reporters on Thursday.
"At this stage we're certainly thinking that will stay at the three-week mark."
Voss said he is "really comfortable" with the approach the Blues took to managing Cerra, who starred against Collingwood before he was substituted out.
"We felt like we were really conservative the week before," Voss said.
"He completed a full week of training and we certainly felt like he was ready to go.
"I guess it's one of those situations where something else happened."
Carlton's current timelines will have Walsh and Cerra back in a full-strength midfield before the finals, should the Blues qualify.
Key defender Mitch McGovern is also expected to miss up to three weeks with his latest hamstring setback.
McGovern suffered a "low-grade strain" at training on Thursday.
Carlton have broken back into the top eight as they aim to end a decade-long finals drought and can extend their winning streak to seven matches when they take on St Kilda at Marvel Stadium on Sunday.
No.3 draft pick Paddy Dow will return to the starting line-up against the Saints, Voss said.
Dow has been the substitute in five of his six appearances this season, including in two of the last three weeks.
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