Kello spent some time with the struggling Championship club in pre-season, appearing in a 2-0 friendly victory over AFC Telford United, but a permanent deal could not be agreed.
The 31-year-old was born in the Czech Republic but qualifies for Slovakia and has three caps to his name for his adopted country.
He agreed to an early release from his contract at Hearts in April 2012 after making 86 appearance since signing from Lithuanian club FBK Kaunas in 2008.
During his four years in Edinburgh the keeper established himself as a firm fans' favourite but found himself frozen out of then-boss Paulo Sergio's plans after rejecting a move to Austria Vienna on the last day of the January transfer window in 2012.
After failed trials with Wolves and Ipswich, Kello joined Romanian Liga I club Astra Giurgiu after a successful 10-day trial and made his debut on October 5 in a 1-1 home draw with FC Vaslui.
However, he found first-team opportunities there limited, with Romania international Silviu Lung Jr firmly established and was released in December after making just two appearances in total.
Wolves require back-up for their goalkeeping spots with Carl Ikeme breaking his hand after punching a tactics board during a recent half-time row and Wales' Wayne Hennessey still recovering following a second operation to repair cruciate ligament damage.
With only Dorus De Vries and Aaron McCarey available as fit keepers and with the emergency loan window near to closing Saunders said: "I've got a keeper here on trial now - a Czech keeper, Marion Kello, and he's been here since Tuesday and he's here until Thursday.
"I don't know how that one will go yet but he's here."
Former Doncaster boss Saunders requires a massive effort from his new team as the Molineux club attempt to avoid embarrassing back-to-back relegations.
Whilst assessing free agent Kello, Saunders also remains on the lookout in the loan market ahead of the deadline.
"We're still right in the middle of (loan window) now and have been seeing if we can get anything through," added Saunders.
"We're trying as we speak, because we're a bit short up front and we've lost Bakary Sako and Dave Edwards so those without those two and Carl Ikeme, Wayne Hennessey, Razak Boukari and George Elokobi, we're looking a bit short in certain areas.
"But I'm trying to do something about it right now."