Capel, 27, has played twice for the Spanish national team and is entering the last year of his contract at the Portuguese side and could be available for a next to nothing price.
Everton boss Roberto Martinez has already addressed problems from last season, by bringing in Gerard Deulofeu to add pace and depth in the winger position but Martinez could be required to add further, should clubs add to their interest in Mirallas by making bids for the player.
Everton have already rejected two bids from West Ham United for the Belgian.
Numerous clubs are chasing Kevin Mirallas this summer
Mirallas has already been linked with a number of clubs this summer, including Monaco and Olympiakos, and Everton could be required to look at replacements for him.
Everton already have similar players like Aiden McGeady and Deulofeu who match Mirallas' pace, but the Toffees would have to look at a player who can also replicate his goal scoring ability.
Should Mirallas leave, Everton would be back down to the bare bones in the wide positions.
If Steven Pienaar is able to beat his injury problems of the past few years he could fit back in at left wing, but he is already struggling to stay fit this pre season. Pienaar brings a different style to Mirallas; he is a classy winger who links up with Leighton Baines and adds more creativity than goals to the team.
Everton have also been linked with Aaron Lennon who had a successful loan spell last season and could be available after he has reportedly been told he can leave Tottenham Hotspur, but Everton are unwilling to match the London club's £9 million asking price.
Lennon’s contract with the club is up after this season and Martinez could be ready to wait to make a move for the winger when this contract is up.
Everton, however, could still be looking at a loan spell for Lennon towards the end of the summer transfer window if he is still unwelcome at Spurs.
Capel would add European experience to a team looking to get back into Europe this season
With Martinez stating that his ambition for next season is to get back into Europe, the addition of Capel, who has played in both the Champions League and Europa League, could help the high number of young players in the Everton squad who have little to no European experience.
Martinez has already added similar experience this summer too, bringing in Tom Cleverley and Deulofeu.