Sandaza was United's top scorer last season following his move from Valencia B so manager Peter Houston believes having him available is a massive boost.
He said: "Fran has done well in training so he's in the frame for Sunday.
"Obviously, he's not fit enough to play the 90 minutes because he's not kicked a ball all season.
"But he'd manage a wee bit and that's a big boost for us and for him."
United face a Jambos side reinvigorated by the return of Jim Jefferies to Tynecastle and the veteran manager has secured enough good results for them to believe they can still challenge for third place.
Houston, who worked with the Hearts boss during his first spell in charge of the club, predicts an open encounter.
He said: "Hearts are desperate to catch up with us, Hibs and Motherwell ahead of them.
"Jim will have them well organised and up for it so it's going to be difficult.
"Since I came to the club, the games we've had against them have been very tight and there have not been many draws.
"So both teams will be going all out to win, that's for sure."
Andy Webster is fit to play after coming off at half-time during Scotland's 1-0 victory over the Czech Republic on Wednesday but Danny Cadamarteri misses out.
Houston said: "Andy Webster has trained so he'll be available, but Danny Cadamarteri won't be available."
Meanwhile, Houston also joined the chorus of SPL managers willing to discuss an enhanced SPL.
The Premier League have indicated they are willing to talk to Division One clubs about expanding the top division and the United boss thinks that is a good plan - provided the financial implications are good.
He said: "I'm very open-minded about it and if someone comes up with a plan which is workable then I think we should all sit down and discuss it.
"Obviously, there are a lot of considerations. From a manager's point of view, it would be great to expand the league and bring more teams in.
"The likes of St Johnstone, Hamilton and St Mirren have all come up in recent years and did really well so the standard is there, no doubt about that.
"And from the playing perspective, it would be refreshing to bring new teams into the set-up.
"There are a lot of big clubs, like Dundee, Dunfermline and so on, who could easily make the step up.
"But, like with everything else, there's a financial aspect to it.
"If Rangers and Celtic are coming to your place twice, that would have to be made up.
"We all understand that money is tight in the game just now so the chairmen would have to be satisfied that any new plan wouldn't affect the revenue.
"But it's something which should definitely be discussed."
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