This may take more than a few events to get this affect. Can you try...
Player > is overlapping object - (add floor object)
(Add condition(s) to test if there are any more objects the player can walk on- if not, do not add the condition) - 'action' > play "walk animation"
Keyboard > on key pressed (jump) - player > play "jump animation"
If that does not work, you could trying adding groups...
Group > controls
Add your movement actions here...i.e - move player logic --- Move 2.5 pixels forward and Set animation "Walk".
Apple Physic force (0,325) and set animation "Jump".
Sub-group > walk animation (only add - on right key pressed > play "walk animation" events/actions
Sub-group > jump animation (only add - on key pressed > play "jump animation" events/actions
Then, still in that 'controls group' but under the sub-groups add...
On key pressed > jump
Condition > player overlapping floor object (invert) disable sub-group > walk animation
I may try and test this later, once i get back to my laptop.