Keenan, a 25-year-old left-back, who began his career at Chelsea, was playing in Australia last season.
The defender, who also had a spell in Holland with Willem II, struggled to hold down a place at Melbourne Victory.
But Paatelainen said: "Joe has done very well, he has great levels of fitness and is very enthusiastic. It's looking positive."
Former Gretna midfielder Yantorno was offered the chance to prove his fitness at Hibs after sustaining knee ligament damage in January.
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The 25-year-old Uruguayan has been using the facilities at Hibs since April and has been working hard on his rehabilitation over the summer.
"He is doing fantastically and improving well," said Paatelainen.
"In a couple of weeks, he should be able to join in with full sessions.
"He will be looking forward to that since it's been a long spring for him.
"He's an exciting player and hopefully he'll get to full fitness and play for Hibs."
Paatelainen snapped up defender David van Zanten under freedom of contract from St Mirren but has lost the services of midfield playmaker Guillaume Beuzelin, who left to join Coventry City.
Dermot McCaffrey, Keegan Ayre, Abderaouf Zarabi, Patrick Noubissie and Mickael Antoine-Curier have also moved on.