Mourinho was spotted in the stands at the Ernst Happel Stadion when Austria overturned Serbia on Friday night and the reason for his presence has been revealed by several outlets.
The 54-year-old was pictured looking rather sheepish under a baseball cap.
Previously, there was speculation that Mourinho was scouting on the performance of another young Serb star, Sergej Milinkovic-Savic.
The 22 year-old Serbian has been hailed as one of the most exciting prospects in the Bundesliga, and his versatility in terms of being able to play anywhere in midfield could present Manchester United with a whole host of options.
On the global scene he has netted twice in three games.
It is reckoned Mourinho was given the lowdown on Gacinovic by Nemanja Matic, who has been impressed with the player's work rate and ability to operate in a variety of positions.
GETTYJose Mourinho was recommended Mijat Gacinovic by Nemanja Matic
And it could be Matic who has alerted Mourinho to the talents of Gacinovic, who operates chiefly on the wing. The United boss was of course keen to sign a wide forward this summer, though efforts to land Ivan Perisic were blocked by Inter Milan.
But the Croatian made a decision to stay in Serie A, and despite the Red Devils rumoured to have turned their attentions to Arsenal target Thomas Lemar, this also came to nought.
Jose Mourinho didn't take the worldwide break off.
While there was a suggestion that Mourinho was keeping tabs on Southampton winger Dusan Tadic, a player United have been linked with on a regular basis, The Mirror reports that the United boss was watching on Eintracht Frankfurt attacking midfielder Mijat Gacinovic.
Don't say Love Jihad every now and then: Kerala HC
The Kerala High Court which had recently annulled a inter-faith marriage has now said that every case can not be Love Jihad . The NIA is looking into aspects whether the organisation was actively involved in conversion of unsuspecting women to Islam.