The Brazilian is being linked with a £15 million summer move to Chelsea this week.
Firmino recently penned a new deal to 2018 with Hoffenheim, but Heldt believes they could still sell this summer.
"He has a highly professional management team, which knows the ins and outs of the business," said Heldt.
"They know exactly at what time he extended his contract and also what opportunities there are to get out of a contract during a contract term."
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