Shaw suffered the concussion in England’s defeat to Mata’s national team, Spain, after a first-half collision with Dani Carvajal.
Mata praised England’s performance despite the loss, but his main concern was the health of his teammate and friend Shaw.
He wrote on his blog: “One of the biggest fixtures of the opening games was without doubt England vs Spain, which finished 2-1 in our favour.
“It was a great result, although England didn’t give up until the final whistle in an attempt to at least take a point.
“The worst news from that match was Luke Shaw’s collision, which forced him off the field due to injury.
“As you’re all aware, he has been in really good form over the last few weeks, I hope that it won’t be anything serious and that he can be back fit as soon as possible.
“I’m sending you a big hug and my best wishes, Luke.”
Shaw made his professional debut at just 16 years old, coming off the bench for former club Southampton in the 2012 FA Cup.
He went on to appear 67 times for the south-coast club before moving to Old Trafford in the summer of 2014 for a fee reported to be in the region of £30m.
After a successful first season at United, he started his second in flying form but was the victim of a serious double-leg break in a Champions League group-stage match against PSV Eindhoven in 2015.
He returned to action after just less than a year but found it hard to recapture the form he had previous to the leg break.
For the first time since the injury, he has looked back to his best self this season so fears and sympathy came in full supply after the head collision on Saturday.
Fortunately, he will only miss two games and Mata’s teammate hopefully should not take long to rediscover his form as United’s best player so far this season.
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