"Zeman will go Roma, but a piece of his heart will always be in Pescara," Sebastiani told Radio Mana Mana Sport.
"His choice (to go to Roma) was inevitable, because returning to the capital was too attractive an offer for him."
Ansa news agency reported that Zeman and Roma had not yet reached agreement over his contract and transfer targets.
However, Roma's managing director Claudio Fenucci made confident noises to Roma Channel, the club's official television station.
"Soon we will formalise the agreement with our new coach and from there will begin the building of a team that I hope this year will give great satisfaction to our fans," Fenucci said.
"We would like to move our project of a spectacular and fun team forward."
Zeman, who was born in Prague but is a naturalised Italian, managed Roma between 1997 and 1999, and the flamboyant style of football his side played left a deep impression on their supporters.
Pescara were promoted to Serie A last season with a team that drew plaudits for their attacking style.
Roma lost 14 league matches last season under Luis Enrique and failed to qualify for European competition.