Mata hasn't featured since Manchester United's victory over Middlesborough last month.
The 28-year-old could be unavailable for the rest of the season after undergoing surgery on a groin problem.
He watched on as Jose Mourinho's side eased to a 3-0 victory over Sunderland yesterday.
Manchester United star Juan Mata admits he is finding being out injured tough
And he admits the victory at the Stadium of Light made his week slightly better.
"When you’re injured you feel like time goes by very slow," Mata said.
"That’s the truth.
Jose Mourinho baffled by Man United's Diego Forlan chant
Mon, April 10, 2017
Jose Mourinho looked absolutely baffled when Manchester United fans started the Diego Forlan chant during their win over Sunderland yesterday…
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Jose Mourinho got a bit confused when United fans sang the Diego Forlan chant
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"And my week seemed longer than usual.
"But luckily it ended with a nice feeling – watching the team’s convincing victory against Sunderland.
"I hope that things keep going well and I can be back soon to enjoy what I like so much – training and playing football."