The former England winger, who was selected in the Premier Sports Team of the Week after scoring two tries in last week’s 28-24 defeat against Sheffield Eagles, landed awkwardly after catching a kick.
But despite the concern over Calderwood, Charlton remains in confident mood.
He said: “We have three winnable games coming up in the next month against teams that will be around us in the table. We’ve got to be looking to be picking up points.”
Holt said: “Our performance against Batley was a big step forward. For the majority of the game we came out on top.
“It should be a benchmark performance for us, and we should be looking to improve each week on it.”
On Workington, Holt added: “We played each other four times last year and while there are some new faces on both sides, these games always follow a similar pattern.
“Workington have gone well at home this year. We’ll look at DVDs and see if there’s anything we can exploit, but we know it will be a big test for us.”