Sherwood can understand Duncan's choice.
He told Sky Sports: "There's been a trend where young English players believe they're not going to get an opportunity at their clubs when they come through the academy.
"It's difficult for Bobby to come in, in front of Salah, Mane and Firmino and they aren't leaving anytime soon.
"So, Bobby feels like it's the right time to go - he's got quality and he needs to play. U23s football is not really the right platform to develop.
"Maybe a loan to Championship would have been good or possibly other teams in the Premier League might have had a look at him.
"But, all credit to him. It's worked for many other English players who have gone abroad and become international footballers so hopefully for Bobby's sake he makes a go of it."