The Manchester United-Bournemouth game in the last round of the Premier League on Sunday was suspended following the discovery of a suspect package in the stadium, reports Efe.
"We were all shocked by what happened at Old Trafford on Sunday," Mata wrote in his weekly blog One Hour Behind on Monday.
"We all had a strange feeling; a mixture of tension and misunderstanding," the Spanish player added.
Mata noted that the performance of all people in charge of security was "efficient and there was a rapid evacuation of the stadium" which helped not to spread panic".
The match between United and Bournemouth was postponed shortly before the start and is set to be played on Tuesday.