Both players picked up injuries during Saturday's 23-7 victory in Melbourne as England secured their first-ever series win in Australia.
Haskell sustained a foot injury while Nowell suffered mild concussion, but Jones is confident that both will be fit to feature as his side chase an unprecedented series whitewash.
"It is more of a precaution with Haskell at the moment. He hasn't trained much over the last couple of weeks, but he has an amazing capacity to absorb pain so he's still in contention for the weekend," he told reporters.
"Jack has cleared all his protocols so far, so there is no reason why he shouldn't be fine. We had a good recovery session on Monday morning. The boys enjoyed the warm Pacific Ocean and a bit of volleyball on the beach.
"It is the third Test of the series so we are going to need energetic, physically aggressive players. The 23 who show they want to play like that are the 23 who are going to play. All the players are keen to play. If they weren't keen to play, they wouldn't be here. We just have to keep assessing them. We'll look at their energy levels over the next day or two in training."
England will be looking to maintain their 100% record under Eddie Jones with victory in Sydney.