Danny Rose came on for Shaw at left-back as the tempo of the match slowed immediately following the Manchester United player being carried off the field, with neither side fashioning any real chances in the following 15 minutes.
Shearer, the Premier League's record goalscorer on 260, believes Rashford has the potential to become a top-class finisher but thinks that is nearly impossible under Jose Mourinho at United.
De Gea produced an acrobatic save to deny Rashford a second goal shortly afterwards but Spain ended the half on top.
The 23-year-old sent in an exceptional pass for Marcus Rashford's opener on his first global start since September 2015 - an appearance that came just a week before the ugly injury that he recently revealed almost cost him his leg.
Not only did the quality of his delivery take out two Spanish defenders but goalkeeper David De Gea did not know whether to come or stay and Rashford gleefully took advantage with a first-time finish.
Rashford missed two other good opportunities in the loss to Spain, in which goals from Saul Niguez and Rodrigo Moreno secured the victory for the visitors, but midfielder Jordan Henderson thinks the forward looks to be in encouraging shape.
Spain, who bowed out in the World Cup last-16 after a torrid campaign, nevertheless showed the benefits of a long-established identity and a level of creativity sorely lacking in England's midfield.
Shaw's United career has been overshadowed by injury. The keeper was perhaps fortunate referee Danny Makkelie deemed he was fouled by Welbeck before the Arsenal striker tucked home late on. "We are building and that is all we can do, play against these teams".
"It was a great tournament for us, but for the gaffer as well and he had a lot of good memories from that". We were a bit disjointed in our pressing, but even when you press well against them they have some wonderful players.
England reached their first World Cup semi-final in three decades in Russian Federation, before losing 2-1 to Croatia.
"We are under no illusion that Spain were the better team for long periods", he said. "Now we can go on and improve".