Motlop, 28, endured a difficult time both on and off the field last season and requested a trade out of Alberton during last month's exchange period.
A deal could not be done, leaving him with little choice but to try and resurrect his career with the Power.
Cornes, who turns 31 this week, also struggled for form last season and was sent back to SANFL club Glenelg in the latter part of the year.
The dual All Australian started his post-season break early after having surgery to repair ligament damage to his finger, but has been back in full training for several weeks.
The premiership player spent significant time in the boxing ring over the break to recondition himself and Cassisi said the star utility was in impressive shape.
"Chad is in great condition," Cassisi said on Wednesday. "He's come back ready to go and is looking really good…and Motts is as well.
"I spent a bit of time at the club over the off season and whenever I was there Chad was there too. Motts was also around doing some work and a lot of the young guys too.
"Coming back reasonably fit at this time of the year gives you a great springboard to have a good season and those two are the standouts so far."
Forward Brett Ebert could also be on track for a round-one return, after rupturing the anterior cruciate ligament in his knee against Melbourne in round 21.
Ebert, 26, followed teammate David Rodan's lead in having LARS surgery to repair the damage and is 11 weeks into his recovery.
Cassisi said the one-time leading goalkicker had also worked hard to maintain his fitness over the break.
"Ebo's already started running and he's lost a fair bit of weight, which is going to be great coming back from a serious knee injury," Cassisi said.
"It's great for the young guys to see his work ethic after going through a bit of adversity."
Injury-prone midfielders Robbie Gray and Hamish Hartlett will also be monitored closely this summer.
Hartlett, 20, was limited to four games last season because of persistent soft-tissue injuries, while Gray managed just 11 appearances.
Cassisi said the pair's fitness would go a long way to determining whether Port Adelaide returned to the September stage next year after three years in the finals wilderness.
"It's very important to get games into guys like Hamish and Robbie because that's where a fair bit of our improvement is going to come from," he said.
"I think the club has grown to know what their bodies are like. We'll be a bit smarter about it and Hamish and Robbie will be a bit smarter about it as well and really communicate with the fitness staff."
The Power have invited three local players, South Adelaide's Nick Liddle, Woodville-West Torrens onballer Nathan Daniel and Norwood's Tom Jonas to train with the team ahead of next Thursday's NAB AFL Draft.
Tall forward Matthew Westhoff, who was delisted by the club earlier this month, will also continue to train with the group.
