Police and local authorities in Nijmegen took the decision after intelligence emerged via social networking sites suggesting there would be a repeat of unsavoury scenes involving Rovers fans in Holland over the previous two evenings.
There were clashes in Deventer on Friday night after Steve Kean's men went down 4-2 to Go Ahead Eagles and incidents with Blackburn and NEC followers occurred in Nijmegen last night.
Sunday's game was due to run alongside a fans' open day at NEC's Gofferstadion, and with 8,000 visitors, including families and children, expected a cancellation was chosen as the best course of action.
"I was at the game on Friday and we heard there'd been a minor, minor disturbance between the two sets of fans," Agnew told Press Association Sport
"On the back of that the authorities, including the police, decided to have a meeting ahead of this game at NEC.
"They had intelligence overnight on the Saturday to suggest there'd been some social networking messages both ways (and) that there could be potential violence."
Agnew stated Blackburn would not rush into any action against those involved without having full possession of the facts, but claimed this was uncharted territory for a club with an unblemished record from previous European trips.
"It's too early to say," he said regarding possible sanctions. "We always take advice off the police and authorities, who have a much better handle on these things and report back to us.
"We've never put the blinkers on for this sort of thing. If something official came back then obviously we would act accordingly.
"It's something new to us. We've been in the UEFA Cup four times in the last 10 years and never had any problems before.
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"We've got a very good record of fans travelling abroad. It's a great shame because a number of our fans will have paid money and taken time to come to these games over the weekend and I feel very sorry for them."
An earlier police statement appeared to suggest Friday and Saturday's clashes occurred in Deventer, but Sandra Bronkhorst, spokesperson for the deputy major of Nijmegen, offered clarification that the second incident took place in Nijmegen.
Bronkhorst also claimed NEC fans may have instigated last night's events, although Agnew later said both sides were reluctant to apportion blame for an unfortunate situation.
She told Press Association Sport: "We heard from the police (after) there was a Blackburn match against Go Ahead Eagles on Friday night and some supporters got in some incidents in the city of Deventer.
"Yesterday night [Saturday] a group of around 80 supporters of Blackburn Rovers got into a fight with some 30 NEC supporters in our city - probably caused by the Nijmegen supporters and not by the English.
"The police had some information that both the English and the Dutch supporters had threatened another confrontation today.
"With 8,000 people in the park, a lot of families and kids, and a big threat of another confrontation between the hooligans meant the mayor and Nijmegen and the police decided that's not a good combination so we had to cancel the game for today."
Asked whether English clubs would be welcome for friendly matches in future, Bronkhorst said judgements would be made on a case-by-case basis.
She added: "I guess that's too early to say now . Before we didn't have an information that this would cause trouble because normally the open days of NEC Nijmegen are really friendly.
"We are not used to any incidents in the city. This is the first time we've had to decide on the day itself, so I think it's too early to say and it depends on which information will be present at other matches."