The Dutchman also praised the impact of the Eredivisie side's new head coach Fred Rutten on the Blues' loanees in comparison with his predecessor John van den Brom
Chelsea scout Piet de Visser says Gael Kakuta is making a "remarkable comeback" as he looks to impress on loan at Vitesse.
The 21-year-old joined the Eredivisie side in the summer, but has struggled for appearances this season after making a slow start.
But De Visser has spoken highly of Kakuta's desire to improve as he looks to adapt his game to differing positions - pointing to the example of fellow Chelsea team-mate Tomas Kalas.
"The Chelsea players are closely followed," he revealed.
"It's noticeable that these guys have made a special development in the first half of the season. Kalas, who spent his whole life playing centre-back, is a revelation as right-back.
"Kakuta was almost amortised by his wrong choices, but is making a remarkable comeback."
Fred Rutten replaced head coach John van den Brom for the start of the campaign, and De Visser has praised the guidance the former player has had on the team in comparison with his predecessor.
"The best example is perhaps Patrick van Aanholt," he added. "Last season he had a dramatic year. John van den Brom [Vitesse coach last year] saw only his nonchalance and then let him not play.
"That was a big mistake. Fred Rutten has started working with him and now he's making great strides. That makes me, but also Chelsea, very happy with Rutten as coach."