"There is no player in Portugal that can replace him".
But the club's manager, Silas, is confident he will be able to call on Fernandes one last time, despite the 25-year-old agreeing personal terms with the Red Devils.
United have held talks with the Portuguese side about signing the midfielder this month, but a deal between the clubs is yet to be reached.
"The only certainty I have is that Bruno will be present", Silas said in Thursday's news conference when asked about Friday's game at the Jose Alvalade stadium.
'We prepared the game with Bruno and he trained very well, as always.
Marcus Rashford has arguably been United's best player in the 2019-20 campaign and leads the club's goalscoring charts with 19 in all competitions.
"I've heard someone say that he's not worth the money you are talking about and it's true, he's worth a lot more". "It's not just going forward but he also kills himself defending". Bruno is the best and the most valuable. Only if there's a disaster he won't be there'.
Silas said there is "no player in Portugal who does" what Fernandes can do.
"If he could score 10-15 goals a season like Paul Scholes used to do or when Wayne Rooney did when he played in the deeper role it would be a great help to the team". There are none in Portugal.
"We would need to find alternative systems [tactics] in order to minimise losing Bruno".
Super-agent Jorge Mendes has been drafted in to accelerate a deal, and was in the Old Trafford directors' box for United's 1-0 win over Wolves in Wednesday night's FA Cup third-round replay.
And Saha has been impressed with what he's seen from the England worldwide and believes that, despite Solskjaer's side being without Champions League football for the time being, he remains happy at Old Trafford.
He is expected to be in the crowd when United face fierce rivals of their own on Sunday afternoon in the form of Liverpool.