Jackson has 72 starts to his credit with the Philadelphia Eagles but has not seen extensive action since 2009. He suffered an arm injury in 2010 and did not play last season.
A planned tryout for the New York Giants this spring did not happen when coach Tom Coughlin said Jackson, 32, was going to retire.
The Cowboys need a center after starter Phil Costa suffered a low back strain on Friday. Costa will not play Monday at Oakland but the team hopes he will return to practice next week. David Arkin will start at center.
Bill Nagy will visit a foot specialist next week because of a high right ankle sprain that could knock him out for the season. Kevin Kowalski is in a cast because of tendinitis that will keep him out for the preseason of not longer.
If Jackson signs Sunday, the earliest he could practice would be Wednesday because of the three-day acclimation period.