Duka, 24, is in his fifth season in MLS, having scored six goals to go along with eight assists in 82 regular-season games in North America's first division, 59 as a starter, totaling 4,751 minutes.
After playing his first three seasons with the Columbus Crew, from 2010-2012, Duka donned the colors of the Chicago Fire in 2013 under the management of current Impact boss Frank Klopas. He established personal bests with four goals and three assists in 31 games, 24 as a starter. He was also in the starting 11 for his team's four US Open Cup matches, helping the Fire reach the semifinals.
Nyassi, joined Montreal in 2012, playing in 54 games over the past two-and-a-half years. His first season with the Impact was his best, as he scored six times and assisted on three others in 28 appearances (17 starts). The 25-year-old Gambian winger has 15 goals and 12 assists in his MLS career, which stretches back to 2009.
Nyassi has played nine times for Gambia, netting a single goal. Duka was a regular with US Under-20 and Under-23 national teams, but has yet to earn a call-up for the full national team.