Martin, who drives a part-time Sprint Cup schedule for Michael Waltrip Racing, will drive only at Martinsville on April 7 in JGR's No. 11 Sprint Cup Toyota. Hamlin is expected to need six weeks to recover from the injury, suffered in a last-lap crash last weekend at Auto Club Speedway.
Brian Vickers, who drives a full-time Nationwide Series schedule for JGR, will assume Hamlin's schedule starting April 13 at Texas Motor Speedway. Hamlin is likely to return for the May 11 race at Darlington but could be back a week earlier at Talladega.
"Obviously having to find someone to fill in for Denny is not an ideal situation to have to be in, and when you start a process like this you obviously begin to look at the drivers that are not only available but also able to drive for your race team and manufacturer. We were a bit premature in determining Mark's status past Martinsville, however," JGR president J.D. Gibbs said in a statement. "We're real happy to have the opportunity to get Brian in our Cup cars and with him driving Nationwide for us we think we have some continuity there that is beneficial.
"We really appreciate everyone at Michael Waltrip Racing and Toyota for working with us through this process. The good thing for us is that we have drivers the caliber of Mark and Brian to help fill in until Denny comes back."
Martin and Vickers split driving duties for the No. 55 Toyota Sprint Cup car. (ESPN)