Earnshaw misses England match
The 29-year-old suffered the injury during Nottingham Forest's goalless Championship draw against Doncaster Rovers last weekend.
Although the problem is not as bad as initially feared, scans have revealed the damage will sideline Earnshaw for around a month, ruling him out of the clash at Cardiff's Millennium Stadium on 26 March.
"Robert has a grade one hamstring injury, which is good news for us," said Forest manager Billy Davies.
"We are probably looking at him being out for three or four weeks. Anything above that would have been a disaster for us."