Pompey fear injured Ricardo Rocha could be set for another spell on the sidelines.
The popular defender limped out of the action against Chelsea on Sunday after aggravating a calf problem.
It was the Portuguese’s first match back after being sidelined by the same injury for the Blues’ previous two fixtures.
Rocha has forged an impressive partnership with Jason Pearce at the heart of the Pompey defence, with the duo again shining at Stamford Bridge.
But Michael Appleton is concerned he may have lost the 33-year-old to injury once more ahead of the visit of West Ham on Saturday.
He said: ‘Ricardo had a calf injury towards the end of the Millwall game and was feeling that again. We just didn’t want to take too many risks with him so took him off.
‘Is it the same injury? It looks that way.
‘It looks as though it is the same problem which forced him off against Millwall.
‘We’ll have to see how that one goes.’
Appleton is hopeful Hayden Mullins will be available for Saturday’s visit of the Hammers.
The midfielder was replaced after 67 minutes on Sunday by Erik Huseklepp.
It was an enforced substitution, with the Pompey boss revealing Mullins also had a calf problem.
Appleton is, however, keeping his fingers crossed the 32-year-old will be okay.
He added: ‘Hayden has picked up a little bit of a calf injury.
‘His substitution was more precautionary. It was starting to feel really, really tight.
‘With the West Ham and Cardiff games coming up, those fixtures became more important than risking an injury.’