Kevin Blackwell also has an interest in Birmingham stopper Ian Bennett, and has already looked at ex-Arsenal keeper Rami Shaaban but will tonight start the game with Australian trialist Adam Federici.
Blackwell confirmed in the Yorkshire Evening Post: "I'm still looking at goalkeepers and I'm hoping we can do something sooner rather than later. That's no slight on Scott (Carson) because he has done magnificently well for us, but I still feel we need some experience around him.
"Neil has joined us for a few days and we'll see how things go. I know all about his capabilities as a goalkeeper, he is vastly experienced and is a good man to have around the place, but I just want to see how he goes in training. If things go alright, we'll see what we can do."
While Sullivan is unable to feature, Chris Bart-Williams will make his debut in midfield. The 30-year-old, who cost Nottingham Forest £2.5m from Sheffield Wednesday in 1995, played a part in Ipswich's play-off last season.
He first met Blackwell for talks in May and has now been offered the chance to impress.
The 24-year-old Gudjonnson is also hoping to impress. Leeds were today seeking international clearance in the hope of including him in the starting line-up at Darlington. The Icelandic international, who started his career in Holland with RCK Waalwijk, spent last season on loan at Wolves from Real Betis.
Blackwell will include a further four trialists in United's latest friendly. Australian keeper Feberici, Polish left-back Tomas Rsaza and a French midfield pairing will also get the chance to impress. Blackwell has already handed chances to Craig Hignett and Steve Guppy - they will again feature at Darlington - while Mark Kinsella and Dutchman Brian Tevreden have been released.
The United boss said: "We've got to use these games as opportunities to look at players. We've still not got the squad quite as we want it and I'm going to try and bring players in on this basis and see if they fit the bill. A lot of the Bosmans have now gone, but we might just unearth something and if that works out, and saves us some money that can be spent elsewhere, then that's the way to go."