Goalkeeper Krul has been with newly-promoted Newcastle for over a decade. The Dutchman signed a new contract extension lasting until 2018 last summer and was promptly loaned to Eredivisie giants Ajax having missed most of the Newcastle's relegation season with a ruptured cruciate ligament suffered on worldwide duty. He was then dispatched to AZ Alkmaar after seeing a proposed move to Watford fall through.
Benitez is said to be eager to sign a new goalkeeper during the current window and last month sanctioned the loan exit of Matz Sels to Anderlecht.
Ojo was involved in Liverpool Under-23s side last season and made just two senior appearances for Jurgen Klopp's side.
Armstrong has scored 26 career goals in 96 games, with his most prolific spell being a stint in League One with Coventry City in the 2015/2016 season.
"Newcastle United striker Adam Armstrong is set to join Bolton Wanderers on loan, HITC Sport understands from sources close to the club".
Centre-back Chancel Mbemba has also not accompanied his teammates to Carton House, although that is apparently due to a "visa technicality" rather than anything transfer releated.
An indication possibly of a couple of young inexperienced players maybe seen as having a chance of progressing - Callum Roberts and Victor Fernandez also on the plane earlier today.