Celtic boss Ronny Deila says keeping his best players will take priority over acquisitions in the transfer window.
Chelsea striker Fernando Torres is understood to be set for a return to Atletico Madrid, according to Sky sources.
The full-back, who moved to Tannadice from Queen's Park in 2010, will be out of contract in the summer and needs to hold further talks with manager Jackie McNamara about his future.
He is desperate to stay and recognises that the best way to make up his manager's mind would be to perform well in the next few games.
"The gaffer has spoken to me and talks are still ongoing so we will see what happens," said the 23-year-old in the Daily Record.
"So, the rest of the season is very important to me and I will need to continue trying my hardest to impress the gaffer.
"I would love to stay at the club but I am just concentrating on my football and will let upstairs take care of my contract."
United have only a faint chance of qualifying for Europe after losing 3-1 at home to Motherwell last Friday and Douglas admits they need to improve significantly in the remaining games of the season.
He said: "We know we need to nullify the rubbish starts if we are to give ourselves any chance of getting into Europe.
"There is still loads to play for this season. Nothing is mathematically impossible so as far as we are concerned, we just have to take each game as it comes and try to get as many points as possible."