The former Republic of Ireland youth international has impressed the Tannadice boss after a successful trial period and Paatelainen is now hoping international clearance can be rushed through to allow the 24-year-old to face Tommy Wright’s Saints.
Gunning made 99 appearances for United over the course of three seasons after signing from Blackburn in 2011.
He turned down the offer of a new Terrors deal in the summer of 2014 as he clinched a move to Birmingham. But he played just once for the Blues after tearing knee ligaments on his debut, with St Andrew’s manager Gary Rowett ripping up his contract at the end of last season.
A short stint with Oldham at the start of the current campaign failed to produce a longer deal but Paatelainen believes the former Motherwell man can boost the basement boys’ relegation fight.
Confirming a deal to the end of the season had been agreed, the boss said: “Everything should be done soon. He’ll be available for selection against St Johnstone provided international clearance comes through, which it should. I’m looking forward to working with Gavin.
“I’m sure you all know how aggressive and how good on the ball he is as a defender.
“I know he has had some big injury problems recently but he is fully fit now and he is really motivated to get back to the best level that he can.
“He hasn’t played too many matches recently though so I don’t think he’s 100 per cent fit but he strengthens out defensive department.”
The Finn, meanwhile, insisted reports suggesting he was preparing to bring back compatriot and former Kilmarnock playmaker Alexi Eremenko back to Scotland for a third spell were “not correct at all”.
And he also declined to discuss former Liverpool forward Florent Sinama Pongolle’s chances of clinching a move to Tayside after he too was welcomed in for a trial stint.
“We have had trialists in last week and this week but I don’t want to go into names,” said Paatelainen. “The boys have done well. They’ve come here and showed their talent.
“But I don’t want to start speculating on whether they will get a contract because that’s an endless story.”
However, Paatelainen did admit he was unhappy that United were no closer to confirming the signing of Japan’s World Cup goalkeeper Eiji Kawashima, despite agreeing terms three weeks ago.
The club are still waiting for a work permit for the 32-year-old but Paatelainen admitted he could not put a time scale on the process.
“Of course it’s frustrating,” he said. “We have a player there who can challenge our current goalkeepers but he is not allowed to train with us, even though everything has been agreed.
“It’s just a pity these work permits take such a long time. Surely the system should be a little more efficient and quicker? We’re talking about a professional who will come here and enhance the whole of Scottish football.
“We’re waiting but we must stay patient.”