Boro are enjoying their best start to a season in nine years and Southgate said, "We are not doing any business between now and the end of Monday.
"We felt the most important thing was to hang onto our best players and the size of the squad is just about right.
"That was the key for me, making sure the players we have got are with us. Lots of situations will settle down after Monday and it is good that everyone knows they are here because I want them here and because they have got a big part to play."