The 24-year-old striker snubbed the Gills’ offer, instead signing a three-month loan deal with the Red Devils from Oxford on Monday.
Hessenthaler is eager to add a striker to his ranks and he told the Kent Messenger: “There was an opportunity but he (Pittman) decided to go to Crawley. That didn’t happen and we will keep trying.
“We are not finding it easy at the moment and it is frustrating.”
Watford boss Javi Gracia does not think Abdoulaye Doucoure's form will be affected by his omission from France's latest squad.