The Aviva Premiership champions' poor record at Adams Park continued on Sunday thanks to a 22-12 defeat, with former player Andy Goode kicking 17 points for the hosts.
"We have got Harlequins at home on Saturday and they have been struggling," Deacon told the Leicester Mercury. "We said in the changing room after the game how disappointed we were, but we have to stay positive and the focus is now on Saturday.
"We didn't get enough decent field position. We had one really good chance in the second half and needed to come away with something from that.
"The difference on the day was Andy Goode, the conditions suited his game. The two drop-goals and the kick from 60 metres were the difference. We never really got going or took the opportunities that we had. Conditions made it difficult and we didn't come away with anything."
Tigers slip to fifth in the table following that result.