Haddin, who took on the role of Australian wicketkeeper following the retirement of Adam Gilchrist in March, suffered the injury during the first Test of the tour at Kingston last month.
Cricket Australia said 27-year-old Western Australian wicketkeeper Ronchi would travel the West Indies as soon as possible to provide back-up following scans of Haddin's right hand during the second Test in Antigua.
"Due to Brad Haddin's injured finger and as a precaution against him missing the third Test and a part of the one-day series, Luke Ronchi will join the Australian touring team," national selection panel chairman Andrew Hilditch said.
"The need for Luke to remain with the squad will be decided as Brad Haddin's fitness becomes clearer," he added.
Ronchi, a right-hand bat, scored a century during Australia A's tour of Pakistan in September 2007 and last season hit the fastest hundred in Australian domestic one-day history during a match against New South Wales.