He came on as a half-time replacement for Patrick Bauer who had been taken ill, Diaby getting warm applause from both sets of fans when he came on to the pitch.
Diaby was with Barnsley until he was given a two-year ban from the game in January 2020 after traces of prohibited substance Higenamine were found in a sample.
The multi-lingual central centre-half began training with the Lilywhites towards the end of his ban and signed a short-term contract at the end of January until the end of this season.
North End manager Ryan Lowe told the Lancashire Post: “It was a nice touch when both sets of fans applauded him.
"I spoke to Bambo the night before the game, had a little conversation with him.
"He told me the Barnsley game was what he had been waiting for. It coincided with Patrick Bauer being sick and having to come off, so he got his opportunity.
"I don’t know if he was trying to let Barnsley score with the first header he made! After that he was calm and composed.
"Bambo has got to get better at certain things, he knows that. But it was a good moment for him at Barnsley.”
When Lowe was asked whether Diaby would be offered a new deal, Lowe said: “I will tell you next week.”
Diaby’s debut came as a substitute at Coventry at the end of February, with his first start coming in the 2-1 win over Bournemouth on March 5.
He started the next two games against Cardiff and Luton, then had a spell in and out of the squad before coming on as a half-time sub at Fulham.
In the Barnsley game, Diaby took Bauer’s position in the middle of the back three, with Sepp van den Berg and Liam Lindsay either side of him.
Lindsay was playing in the absence of Andrew Hughes who needed stitches in a gashed toe suffered against Blackburn last week.
Hughes’ fitness will be monitored ahead of Middlesbrough’s visit to Deepdale on Saturday lunchtime (12.30pm).