The former Liverpool captain has been given the honour in just his fourth game since moving to Amsterdam from Al Ettifaq.
Manager John van 't Schip was forced into the decision with captain Steven Bergwijn joined on their injury list by vice-captain Steven Berghuis.
Henderson joins a star-studded list of Ajax captains that includes Luis Suarez, Jaap Stam and Edgar Davids.
Henderson is yet to taste victory in an Ajax shirt, having played every minute available since debuting against league leaders PSV on February 3.
NEC present a good chance of victory at home, but Ajax's last league game saw them lose 3-2 to struggling side Heerenveen.
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Henderson joined Ajax on January 18, cutting short his stint in the Saudi Pro League.
The 33-year-old joined Steven Gerrard's Al Ettifaq in the summer in a £13million deal from Liverpool, but his time in the Middle East lasted just six months before he grew disatisfied.
Previous to his time at Al Ettifaq, where he was also captain, Henderson wore the armband for Liverpool for eight years.
Taking over from club legend Steven Gerrard in 2015, Henderson went on lift the Champions League, Premier League, League Cup, FA Cup, Club World Cup, European Super Cup and Community Shield as captain.
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Henderson's chances of adding to that look slim this season, with a whopping 23 points off the Eredivisie lead, while they drew their Europa Conference League first-leg play-off tie at home to Bodo/Glimt.