According to Pelissero, Martin has a hyperextended knee and a bone bruise. The Dallas Morning News' David Moore had reported the Cowboys received "encouraging" results from an MRI on Martin's knee and that they're hopeful he'll be available for Week 1 of the 2018 regular season.
Dallas opens the year Sept. 9 on the road against the Carolina Panthers.
Martin is coming off his fourth straight Pro Bowl season in 2017. He's a big reason the Cowboys ranked fourth in adjusted line yards last season, per Football Outsiders.
The 27-year-old sat third in Bleacher Report's NFL1000 year-end ranking of the top offensive guards.
"When he engages, Martin latches onto his defender like an octopus and starts pushing back right away," B/R's Doug Farrar wrote. "He's able to match aggression with technique, making him one of the best power-blockers of his generation."
The fact Martin avoided a more serious knee injury is great news for the Cowboys, who signed him to a six-year, $84 million extension in June.
Martin's streak of 64 straight starts may not be in imminent danger either. Since Dallas selected him 16th overall in the 2014 draft, he has yet to miss a game in the NFL.