The 28-year-old has been hampered with injuries over the last 12 months and was reduced to just 15 appearances across all competitions in 2023-24.
Shaw has been sidelined since the middle of February when he sustained a muscle injury in Man United's 2-1 Premier League win at Luton Town.
To the surprise of some supporters, Shaw was included in Gareth Southgate's preliminary England squad ahead of Euro 2024 and the left-back faces a race against time to be ready for the tournament in Germany.
Shaw was in attendance at Wembley Stadium to watch Man United beat rivals Manchester City in the FA Cup final last weekend, and he has since taken to social media to congratulate his teammates, reflect on the season and deliver an update on his fitness.
Shaw hits out at critics amid injury 'frustrations'
In a statement posted on Instagram, Shaw said: "Happy for the boys to lift the trophy at the weekend and finish this season on a positive. As much as it was the result I wanted it was hard to watch from the stands.
"This has been the most frustrating season for me. I have had setback after setback and have worked so hard to get back to fitness but things just haven't gone my way.
"I pushed so hard to get back before the end of the season and the final but some things just aren't meant to be. There's nothing I want to do more than play and win with Manchester United.
"I don't react to things I see on social media but there are a lot of people questioning my loyalty to this club and asking how I am fit for England but not United.
"The reality is I am not 100% fit for either right now but I am doing everything I can and constantly working to be. I have been at this club for 10 years through highs and lows and for anyone to question my loyalty is obviously frustrating.
"I appreciate I haven't updated you all with my injuries and where I'm at with my recovery but equally the most important thing to me is that we're supporting the team playing.
"My biggest focus right now is being fit and then whatever happens this summer I will be ready. Thank you for your patience."
How will England cope if Shaw misses Euro 2024?
Shaw is the only recognised left-back that has been selected in Southgate's 33-man provisional squad, so his potential absence from Euro 2024 would leave the Three Lions light in that position.
Southgate has opted to leave out Chelsea duo Ben Chilwell and Levi Colwill from his squad due to their injury concerns, while the likes of Crystal Palace's Tyrick Mitchell and Newcastle United's Dan Burn have not been considered.
Should Shaw miss Euro 2024, Kieran Trippier would presumably be the most likely candidate to play at left-back as he has experience operating on either side of the back four or five with England.
Joe Gomez is another option at Southgate's disposal and has been called upon to feature regularly in the left-back role under Liverpool manager Jurgen Klopp this season.
Everton star Jarrad Braithwaite, who is yet to earn his first senior international cap, is a left-footed centre-back who could also be tasked with filling in on the left side of defence if needed.
Southgate must confirm his final squad of up to 26 players before June 7 ahead of Euro 2024, with their first group game taking place on June 16 against Serbia.