Rashford was in and out of the United team during 2017/18 but still appeared in 52 of the Reds' 56 games in all competitions - more than any other player - and was involved in 22 goals (scoring 13 and assisting nine).
Over the course of last season, Mourinho opted to play Romelu Lukaku as his only striker. Where would Rashford sit should that move come to fruition?
He also believes they will reach the quarter-finals in Russian Federation and have a chance to do even better.
He said: "There [are] about 30 players in that pool now but I'd prefer it to be around 40, I'd be more comfortable with that". Then they might produce some of the moments we saw from Marcus. "Today he had that exuberance and was teasing defenders".
Though perhaps a better problem to have than others experienced by England managers in recent years, the performance presents something of a quandary for Southgate, posing the hard question: should Rashford start over Manchester City'sRaheem Sterling?
Henderson has been one of Southgate's key performers in the last 12 months, and while he might have missed out on the captain's armband, with his manager turning to Harry Kane instead, the former Sunderland midfielder is desperate to be involved from the outset in Russian Federation.
Southgate must now consider whether the Manchester United forward has done enough to earn a starting shirt against Tunisia on June 18 but would need to rejig his system or drop Raheem Sterling to make room. It was the type of goal that only a player full of confidence can score, which is all the more surprising when you consider that Rashford's first team opportunities at Manchester United this season have been limited. The substitutes began coming and one of them, Danny Welbeck, was on hand to dispatch a diving header after Rashford and Dele Alli cut through Costa Rica's defence.
Danny Welbeck is setting his sights on going past David Beckham in England's scoring charts after underlining his worldwide credentials against Costa Rica. Expectations might be relatively low back home, but there are reasons England have been tipped as dark horses by fans around the globe.
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