Jon is ineligible to play against Fulham because of FA cup rules, but, along with former Fulham defender Andy Melville, who is cup-tied in the 'traditional' sense, will be lending his vocal support to the Hammers.
"To be honest, I will be supporting West Ham because if I go back to Fulham anyway I can't play in the FA cup for them," he says.
"If West Ham progress and I do stay on at the club I can carry on playing in the next round but if I went back to Fulham I would be cup-tied because of the Wolves game I have already played in for West Ham."
It is a rule peculiar to the FA cup that you can't play against the side holding you registration if you are on loan, and leaves Jon frustrated.
"It is a strange rule because Francis Jeffers played against his team in the league but you can't do it in the FA cup," he says.
"I can't argue that, I just have to get on with it."
It is a measure of the buoyancy at West Ham, though, that Jon, an established Premiership player with Fulham and before that Chelsea, is prepared to drop down a division to play for the Hammers on a permanent basis.
"Fulham have told me I can leave, I am having a good time at West Ham, and in an ideal world I would like to stay there, though that is not down to me," he explains.
"My loan is up at the end of the game Saturday, I am just praying that something gets sorted out, because I don't really see that I have a future at Fulham - and I would be happy to stay at West Ham.
"I have had four games and it is three wins and one draw which we were quite unlucky in; it would be nice to carry that sequence on."
Jon believes that if he did drop a division, it wouldn't be for long, and he adds:
"Things are definitely looking good; we are moving up the league and we are in the playoff positions now.
"The mood around the camp is that everyone is aiming to go up directly, not even via the playoffs - which we are capable of doing.
"I think if you look at the league we are still a way off top spot, but there are definitely a few games left in the season and if we can carry on our current form and keep winning games nobody knows what can happen.
"And it is a boost that we played Wolves recently, and have another Premier League side in Fulham at the weekend - hopefully we can go on a good cup run as well."