The 28-year-old forward joined up with Michael Carrick's squad at their pre-season camp in Maynooth, County Kildare, having been given an extended break after helping England reach the World Cup semi-finals over the summer.
Open training sessions were shelved to keep the reunion low-key, and Rashford is expected to sit out Wednesday's friendly against Leeds at Croke Park as he builds up his fitness.
A more fitting stage for his first appearance could arrive next Saturday, when United close their pre-season programme against Ruben Amorim's AC Milan in Poland. It was Amorim who exiled Rashford from the first-team squad in December 2024, a decision that led to loan spells first at Aston Villa and then at Barcelona, where he scored 14 goals and provided 14 assists last season as the Catalan club won La Liga.
Barcelona opted against triggering their £26 million option to sign him permanently, and with three weeks left of the transfer window, well-placed sources say Rashford is now keen to stay and fight for his place at Old Trafford rather than push for another move.
There has been interest from elsewhere in the Premier League, according to The Sun, though nothing concrete has yet materialised. Rashford, who has two years left on a deal worth £325,000 a week, is understood to be reluctant to join Fenerbahce, who have made contact, or move to Saudi Arabia, still harbouring ambitions of playing at the top level in Europe.
Manchester United's other significant issue this window centres on left-back, where Carrick has identified Newcastle United's Lewis Hall as his preferred long-term successor to Luke Shaw.
The 21-year-old wants the move to Old Trafford to happen and has made that clear to those around him, even after Newcastle's appointment of new head coach Matthias Jaissle in place of Eddie Howe. Well-placed sources say Newcastle have taken deliberate steps to shut down the speculation, desperate to avoid losing another prized asset after a summer that has already seen Anthony Gordon, Sandro Tonali and Bruno Guimaraes leave St James' Park.
United have been offered Arsenal's Myles Lewis-Skelly as an alternative, having monitored the youngster earlier in the year, but Hall remains the priority.
He is under contract at Newcastle until 2029, giving the Magpies significant leverage in any negotiation, and United are understood to have belatedly accelerated their interest as they weigh up whether a fresh, improved offer is required to test Newcastle's resolve before the deadline.