Midfielder Gus has travelled abroad to see a specialist after being troubled by his wrist in recent weeks - he's been playing with a lightweight cast on his right arm this season.
Jon misses out with a slight knee injury and caretaker boss David Pleat revealed that the knock has ruled him out of a possible loan move.
"He has a minor knock behind his knee which is giving him a little soreness," said David. "It's unfortunate because a Division One side have asked to loan him and we've had to knock it on the head for the time being. It's a shame because the experience would have been good for him.
"Gus has travelled abroad to see a specialist about his wrist. It has been giving him some trouble but we hope he'll be okay for next week."
Fredi Kanoute (ankle), Jamie Redknapp, Christian Ziege (both knee) and Simon Davies (thigh) are still sidelined although striker Fredi appears to be closing in on a return.
David added: "As long as he's training every day and comfortable I won't necessarily look to give him lots of match practice before he's involved in the group."
Dean Marney, outstanding in Wednesday night's reserve win at West Ham, is back in the squad.
"He gives us honesty and enthusiasm," said David. "He has a little experience in the league at Swindon and was in the squad at the start of the season. He'll travel and whether or not he's substitute, we'll see."
Gus Poyet and Jon Blondel are out of the squad for Saturday's Premiership trip to Blackburn Rovers.