No deals can be finalized with free agents of other teams until Thursday at 4 p.m. ET.
Wagner, 27, is considered the best right tackle in free agency after quietly being one of the Baltimore Ravens' most reliable starters the past three seasons.
Adding Wagner would help accomplish what Lions general manager Bob Quinn said he wanted to do at the outset of the offseason, which is to improve Detroit's stagnant running game that averaged 81.9 yards per game last season.
His likely signing also means the departure of former Detroit first-round pick Riley Reiff, who played this past season at right tackle after spending the prior three seasons as the team's left tackle.
Last season, he produced one of his best seasons since being selected in the fifth round by Baltimore in 2013. He gave up three sacks, four quarterback hits and 25 hurries in 2016, according to Pro Football Focus.
Losing Wagner continues a trend of the Ravens letting young offensive linemen go elsewhere. Over the last five years, Baltimore was unable to keep guard Ben Grubbs, tackle Michael Oher and guard Kelechi Osemele.
ESPN's Jamison Hensley and Michael Rothstein contributed to this report.