Boro rejected two separate offers from Feyenoord for van den Berg earlier this week, with the most lucrative understood to have involved a package worth around €10m.
The Teessiders insist that does not meet their valuation of the 21-year-old, who recently starred for the Netherlands at the European Under-21s Championships.
Feyenoord are expected to make renewed contact with Boro officials in the next couple of days as their need for a new defender has increased after Atletico Madrid agreed a deal to sign David Hancko.
Hancko had looked set to join Saudi Arabian side Al-Nassr last weekend, but that deal collapsed reducing the need for Feyenoord to continue to pursue van den Berg.
Atletico sensed an opportunity, though, and made rapid moves to sign Hancko, which have resulted in a swift agreement with Feyenoord officials.
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Hancko, a Slovakia international, is set to join Atletico for around €30m, and Feyenoord are keen to reinvest some of that money into the signing of van den Berg.
Boro have accepted there is a decent chance of the Dutch defender leaving this summer, but are adamant they will not be allowing him to leave unless their valuation is met.
And until that happens, Edwards will continue to field van den Berg in Boro’s friendly games. The youngster started last night’s 2-0 defeat to Bradford City at Valley Parade as part of a three-man backline, and unless things change in the next couple of days, he will also be selected in the squad that will travel to Ibrox for Saturday’s friendly with Rangers.
“It was an easy decision to play him [at Bradford],” said Edwards. “He’s here, his mindset was great and until I’m told differently or he is, he’s here and happy to be here as well.
“We had a really good conversation yesterday. He said he was keen to play in this one and play for Middlesbrough.”
Boro are on the brink of completing their first signing of the summer, with Alfie Jones set to complete his switch from Hull City.
The defender is moving to the Riverside in a deal worth around £3m, although Boro’s initial up-front payment is understood to be significantly lower than that figure.
Asked directly about Boro’s interest in Jones, Edwards said: “He’s a player I admire, but there are many players we’ve been linked with who I admire.
“Right now, he’s a Hull City player at the moment, so I don’t want to say too much. He’s a very good player though.”