De Gea has been linked with a move to Real Madrid in recent weeks.
The Spain international nearly joined the Spanish club in 2015, only for a deal to fall through due to a faulty fax machine.
He signed a new four-year contract just weeks after the failed deal and scooped the club's player of the year award for the third season running last term.
Premier League stats: Most saves so far in 2016/17
Wed, February 8, 2017
Express Sport reveals which Premier League goalkeepers have made the most saves this season (as of 08/02/17)
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Which Premier League goalkeeper has made the most saves so far this season?
David De Gea has been in fine form for Manchester United this season
David De Gea starred as Manchester United held Liverpool in October
De Gea has helped Manchester United mount a challenge for the top four this season with more eye-catching performances.
And Herrera has singled out his save from Liverpool playmaker Philippe Coutinho back in October as the best he's ever seen.
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"I like to talk about my keeper so the one David [De Gea] did at Anfield this season," he told United Review when asked what the best save he had ever seen was.
David De Gea and Ander Herrera have been team-mates since 2014
"It was a Philippe Coutinho shot and David saved it with his right hand, I think."
De Gea and Herrera are both expected to start when United go up against Watford tomorrow (3pm).
Should Arsenal lose to Hull in tomorrow's 12.30pm clash then a win against the Hornets would propel Mourinho's side into the top four.