The 25-year-old was previously at Liverpool – who he joined in 2010 when he was 17.
Suso failed to make much of an impact at Anfield and joined AC Milan in 2015 when his contract expired.
With the Serie A club, the attacking midfielder has made 135 appearances with 23 goals and 35 assists to his name.
LIVE ON talkSPORT
talkSPORT is your home of live football! Here's what's coming up on talkSPORT and talkSPORT 2…
- England Women vs Denmark Women (Saturday, 1pm) – talkSPORT
- Newport County vs Tranmere (Saturday, 3pm) – talkSPORT
- Charlton vs Sunderland (Sunday, 3pm) – talkSPORT
He has been an important figure for them over the last three seasons, playing the majority of Milan’s fixtures.
The Italian giants have one final Serie A match of the season left and must beat SPAL if they have any hope of qualifying for the Champions League.
They will also be relying on their city rivals Inter to slip up against Empoli for that to happen.