It means that he has no longer been certain of a place in the selection at the Red Devils. While he was almost always there under Roberto Martinez, he was only called up once by his successor Domenico Tedesco. In June he was a starter when the Belgians did not get further than a 1-1 draw against Austria in the European Championship qualifiers at home. Dendoncker then dropped to the center back next to Wout Faes. That was his 32nd cap for the national team.
The West Flemish comes from the youth academy of RSC Anderlecht and ended up in the first team in 2014. Alongside his buddy Youri Tielemans, his teammate at Villa, he excelled in midfield for several years. This earned him a transfer to Premier League club Wolverhampton Wanderers in 2018.