On December 11, 2017, it was announced that Washington had accepted his invitation to play in the 2018 Senior Bowl. Washington impressed scouts and analysts during practices in preparation for the Senior Bowl. On January 27, 2018, Washington played in the 2018 Reese's Senior Bowl, but finished without a catch as a part of Houston Texans head coach Bill O'Brien's South team that defeated the North 45–16. Throughout the game he was covered by Jacksonville State's Siran Neal. He attended the NFL Scouting Combine in Indianapolis and completed all of the combine and positional drills. He finished 14th among all wide receivers in the short shuttle. On March 15, 2018, Washington participated at Oklahoma State's pro day and performed the 40-yard dash (4.50s), 20-yard dash (2.70s), 10-yard dash (1.61s), vertical jump (39"), and broad jump (10'2"). He also attended a pre-draft visit with the Dallas Cowboys. At the conclusion of the pre-draft process, Washington was projected to be a third round pick by NFL draft experts and scouts. He was ranked the seventh best wide receiver prospect in the draft by Scouts Inc. and was ranked the ninth best wide receiver by DraftScout.com.
