Manchester United have not given up on trying to sign the England international, despite missing the August 10 deadline the Bundesliga club set for the deal to be completed.
Sancho did not fly with the Dortmund squad to face Bayern Munich in the DFL-Supercup on Wednesday, with the club confirming he has a respiratory infection. The 20-year-old tested negatively for coronavirus on Monday.
The Dortmund hierarchy have stated on several occasions - before and after the deadline - that if it was not met Sancho would remain at the club, but rumblings have continued over United submitting a bid before the international transfer window closes on October 5.
Earlier on Tuesday, Dortmund captain Marco Reus told Sky in Germany that Sancho is staying for one more year.
Asked if Sancho had made the right call to stay and had the potential to be as good as Cristiano Ronaldo, Reus said: "For us players that was great news.
"We all were happy that he will be with us for one more year because he delivers assists and goals, so we get points.
"If he gets as big as (Lionel) Messi or Ronaldo, we will see. He needs time, experience and it will be important how he manages the times when things don't go so well. But he has the confidence and the quality."
United made a breakthrough in negotiations with Sancho's representatives earlier this month, with wages and agent fees no longer thought to be an issue for the Premier League club, but on September 23 Dharmesh Sheth told The Transfer Show that Dortmund had been left "bemused" by United's attempts to sign him.
United's only signing of the window so far has been central midfielder Donny van de Beek from Ajax, but manager Ole Gunnar Solskjaer has suggested the club are still hoping to do more business.
Man Utd consider Watford's Sarr as Sancho alternative
United are working on alternatives if they fail in their efforts to sign Sancho and have an interest in Watford's Ismaila Sarr.
Watford would only consider a sale and value Sarr at £50m, but any move for the Senegal international does not need to be completed until the domestic deadline on October 16.
United also looking at Barcelona's Ousmane Dembele, but a source close to the player has told Sky in Germany he wants to stay at the La Liga giants.
Pereira close to sealing Lazio loan
Manchester United midfielder Andreas Pereira is close to joining Lazio on loan.
Lazio will have the option to make the deal permanent at the end of the season and will pay all of the Brazil international's wages.
The Italian club's sporting director Igli Tare said on Monday he is confident the United midfielder will join the club "in the next two or three days".
Pereira was left out of the matchday squad for United's first two Premier League games of the season against Crystal Palace and Brighton, as well as for their Carabao Cup tie at Luton last week.
Dark arts of transfers
Football writer Andy Mitten has been questioning Manchester United's waning power in the transfer market and says they have lost the ability to do the "dark arts of transfers" with fans receiving "mixed messages" about the club's financial position.
"It's very frustrating for fans and they've seen just one player come in so far," Mitten told Sky Sports News.
"I don't think anyone has the same pulling power as Sir Alex Ferguson but to be fair to Ole, he's been putting calls in and I know he's spoken to several managers about players who he likes."
Neville: Man Utd 'negligent' over signings
Gary Neville has had some strong words concerning United's recent transfer policy.
After their 3-1 loss to Crystal Palace in their first game of the season at Old Trafford, he told the Gary Neville Podcast that his former club could miss out on a top-four spot if they failed to bring in some new faces.
Summer transfer window - key dates and times
The summer transfer window closes at 11pm on Monday October 5 with a feast of activity lined up on Transfer Deadline Day on Footy Legend.
A domestic-only window for deals between the Premier League and EFL then runs from October 5 and closes on Friday October 16 at 5pm.
Source: Sky Sports