The Argentina captain's long-awaited transfer to the Spanish club is expected to be completed in the next 24 hours after the Reds accepted a suitable bid, having rejected a £16million offer last weekend.
When news of that approach reached the 26-year-old he backed out of playing in the Barclays Premier League defeat to Manchester City at Eastlands on Monday.
"It is not easy for me to defend the actions (of Mascherano) because professionals are paid to play and when they are called on to play, they play," he said.
"We had a player at Blackburn, Graeme Le Saux, who was very agitated when I joined the club because he was determined to go to Chelsea and that caused a lot of problems in pre-season.
"Tim Sherwood was wanted by Tottenham and that caused a lot of problems because he wanted to get back to London.
"These situations do occur unfortunately and we have to live with it.
"I don't think they (the players) mean it as a challenge to your authority or a challenge to the club's authority.
"It is just a selfish situation that they have got something they want to do and they just expect the club, and therefore you as one of the leaders of the club, to bow down and accept that they are going to do it.
"Unfortunately there are going to be periods of time when there will be some unpleasantness because players must also understand that when you sign contracts you sign contracts to play.
"If the club decide they are going to accept an offer for you and let you go that is one thing, but you run the risk the club might say 'I'm sorry, you've got the contract and we aren't selling you so you are staying'.
"It doesn't bother me as a challenge to my authority it is just a fact of life.
"But it is a fact of life which gets exacerbated in a one-month period in January and between July and August when it is a time of year when a lot of people are trying to do their business."