Arizona Cardinals coach Bruce Arians required hospital treatment for the second time in four months after his side's defeat to the Minnesota Vikings on Sunday.
The 64-year-old experienced discomfort and his wife took him to the hospital on Monday, the team said in a brief statement.
All tests conducted so far have come back "favourably," the team said, but he remains hospitalised for evaluation.
In August, Arians was taken by ambulance from the Cardinals' and San Diego Chargers' joint practice after experiencing stomach pain.
Arians is a prostate cancer survivor but has been in good health since missing one game in 2012 while serving as interim head coach of the Indianapolis Colts with an ear infection.
The Cardinals (4-5-1) suffered a 30-24 loss to the Vikings on Sunday and are in danger of missing the playoffs for the first time in three seasons.