The LA Galaxy, in need of help up front, signed McInerney, 24, after he cleared waivers.
It's his sixth MLS club in eight seasons.
McInerney scored five goals in 24 appearances last season for Portland, which waived him March 1, and has tallied 43 MLS goals and registered six assists in 167 league games since starting his career with Philadelphia in 2010. In his most productive season he scored 12 goals in 2013.
“Jack is a young and experienced player in MLS who has shown that he can score goals in this league,” said Galaxy general manager Pete Vagenas in a club release. “He will give our team valuable depth at the forward position throughout the season. We look forward to Jack joining the team this week ahead of Sunday’s game.”
McInerney has been added to the Galaxy roster and is eligible to play against Seattle at StubHub Center this weekend. Giovani dos Santos has only one goal this season while Gyasi Zardes has yet to score since returning to action.
The Union, then an expansion team, used the No. 7 overall selection in the 2010 SuperDraft to select McInerney, a native of Chattenooga, Tenn., who scored two goals for the U.S. at the 2009 U-17 World Cup in Nigeria.
He scored 25 goals in five seasons for Philly, which after the 2014 season traded him to Montreal. With the Impact he notched 11 goals in 43 games prior to a trade during the 2015 season to Columbus, with which he scored two goals in five games.