I'm going to go with Alvin Williams (so, obviously I'm interpreting the question as "for up to a whole season")
Portland Trail Blazers Players | Basketball-Reference.com Sort by years and see what you see. Played before my time, but Jim Barnett might be the most impactful 1 season player in Blazers history.
Barnett is probably the 'right' answer. However, Leroy Ellis was a decent big man back when big men had value. Of course, that was Portland's first season in the league
I enjoyed Jingles twitter exchanges with Hart, but as it has been and always will be... winner winner, Travis Diener. Simply because I can write winner winner, Travis Diener.
Pack or Curry for me. Cant decide which though. I think Curry is an option based on recent memory. But I bet if i go back and watch Pack highlights i would choose him as a stand alone.
Pack Man went on to Denver and is a cult hero there. But he was just as loved in Portland. Everyone i knew at that time was singing the praises of Robert Pack in PDX.
I used to love those Rumeal Robinson 10 day contracts back in the mid 90’s. Some of you young bucks might not date back that far