Derby County first-team coach John Peacock has described Dutch goalkeeper Kelle Roos as "one for the future".
The 23-year-old joined fellow Championship side Rotherham United in a season-long loan deal earlier this month, alongside his 21-year-old Rams team-mate Farrend Rawson.
Peacock told BBC Radio Derby: "I think the next level for Kelle is to try to challenge himself a bit better.
"Moving to a Championship club like Rotherham will certainly enhance that."
When asked about Rawson's loan, Peacock added: "I think he enjoyed the experience [at Rotherham]. It can only benefit him and I'm sure it will aid his development going forward."
Peacock, who was director of Derby's academy from 1998 until 2002, said that he and new manager Paul Clement were aware that there may be further departures.
"The manager and myself are getting to know these players," he said. "Decisions will be made, and some tough decisions will be coming up very shortly when the season starts.
"If you want to get anywhere in this division you have to have a strong squad and maintain a sense of competition."