Tomkins made the switch of codes last season, joining from Wigan Warriors, and played just four times in the Aviva Premiership.
But now that he is fully acclimatised to the union, Gustard is expecting big things from Tomkins, the brother of league superstar Sam.
"I am expecting big things from centre Joel Tomkins this season," Gustard told the Rugby Paper.
"He is good pals with Chris Ashton and I think he has high expectations of himself.
"We made a deliberate point of signing him midway through last season so he would have a few months to acclimatise to the demands of union.
"It means he comes into pre-season fully understanding all the intricacies of the breakdown and the other regulations so he is, in effect, on a par with every other player.
"We desperately want him to be a success in union not just for Saracens but for England as well. He is 6'3, 15st 7lbs, is lightning quick and is a brilliant offloader - that is a skillset for an outside centre that would benefit any international side.
"You obviously have Manu Tuilagi who is a very different beast, but I think Joel could be a huge success for England."
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The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
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