The Western Conference sides look to enter MLS' summer break with a winning streak.
Both clubs secured wins last season as they jockey for position ahead of the two-week break in the MLS schedule. Dallas (6-7-3) topped Colorado, 3-2, last week to snap an eight-match winless streak while Portland (4-4-7) snagged a 3-1 road win against Real Salt Lake.
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Despite Dallas' poor recent form, it is the visitors who go into Wednesday's match in the playoff positions, thanks to a hot start that cooled when playmaker Mauro Diaz was lost because of an injury. He remains out long-term, as does defensive midfielder Hendry Thomas.
For the hosts, Michael Harrington is questionable while Rodney Wallace is continuing recovery from ACL surgery while on loan at USL Pro club Arizona United.
Dallas will look to cool Fanendo Adi, who scored twice in Portland's weekend win, and the Timbers will try to keep Fabian Castillo from putting in a second consecutive man of the match performance.
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