Although Sanchez helped orchestrate his side's recent wins over Manchester City and Swansea City, he could do little to prevent his side from suffering an embarrassing 1-0 defeat to West Brom to officially end their hopes of winning the league title.
The 29-year-old was subsequently an unused substitute in Wednesday's 2-0 win over Bournemouth as Mourinho opted to start Anthony Martial on the left alongside Marcus Rashford and Jesse Lingard in attack.
As the Red Devils gear up for their cup tie with Mauricio Pochettino's side, Alexis is expected to return to the first-team this weekend, but ex-United and England midfielder Scholes believes Mourinho should leave him out again.
"I think the big decision is who plays either side of Lukaku," he said on BT Sport. "I'd go Rashford and Martial but I think he will probably bring Sanchez back into it.
"I just don’t think his form has been good enough. I think he’s been quite predictable – we all know the talent he’s got.
"Obviously there is a magnificent player in there but at Manchester United he’s just not showing it yet. I think Martial and Rashford are better options."
Martial has nine goals and five assists to his name in 27 Premier League appearances this term, while Rashford has six in 30 games.